cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

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A242614 Triangle read by rows: row n contains numbers with sum of digits = n, and not greater than the n-th repunit (cf. A007953 and A002275).

Original entry on oeis.org

0, 1, 2, 11, 3, 12, 21, 30, 102, 111, 4, 13, 22, 31, 40, 103, 112, 121, 130, 202, 211, 220, 301, 310, 400, 1003, 1012, 1021, 1030, 1102, 1111, 5, 14, 23, 32, 41, 50, 104, 113, 122, 131, 140, 203, 212, 221, 230, 302, 311, 320, 401, 410, 500, 1004, 1013, 1022
Offset: 0

Views

Author

Reinhard Zumkeller, Jul 16 2014

Keywords

Comments

Number of terms in row n = A242622(n);
T(n,1) = A051885(n);
T(n,A242622(n)) = A002275(n);
for n > 0: number of repdigit terms in row n = A242627(n).

Examples

			The triangle begins:
. 0:  0
. 1:  1
. 2:  2,11
. 3:  3,12,21,30,102,111
. 4:  4,13,22,31,40,103,112,121,130,202, . . . ,1021,1030,1102,1111
. 5:  5,14,23,32,41,50,104,113,122,131, . . . ,11021,11030,11102,11111 .
		

Crossrefs

Programs

  • Haskell
    a242614 n k = a242614_row n !! (k-1)
    a242614_row n = filter ((== n) . a007953) [n .. a002275 n]
    a242614_tabf = map a242614_row [0..]
  • Mathematica
    Join[{0},Flatten[Table[Select[Range[FromDigits[PadRight[{},n,1]]], Total[ IntegerDigits[ #]] == n&],{n,5}]]] (* Harvey P. Dale, Oct 08 2019 *)

A187813 Numbers n whose base-b digit sum is not b for all bases b >= 2.

Original entry on oeis.org

0, 1, 2, 4, 8, 14, 30, 32, 38, 42, 44, 54, 60, 62, 74, 84, 90, 98, 102, 104, 108, 110, 114, 128, 138, 140, 150, 152, 158, 164, 168, 174, 180, 182, 194, 198, 200, 212, 224, 228, 230, 234, 240, 242, 252, 270, 278, 282, 284, 294, 308, 312, 314, 318, 332, 338, 348
Offset: 1

Views

Author

Tom Edgar, Aug 30 2013

Keywords

Comments

Except for 1, every number is even.
No number ends in 6.
Numbers neither in A018900 nor in A226636 nor in A226969 nor in A227062 nor in A227080 nor ... . - R. J. Mathar, Sep 02 2013
From Hieronymus Fischer, Mar 27 2014, May 09 2014: (Start)
A079696 and this sequence have no terms in common.
Numbers which satisfy m == 1 (mod j) and m > j^2 for any j > 1 are not terms.
Example 1: m = 10^k, k>1, is not a term since 10^k == 1 (mod 9) and 10^k > 9^2.
Example 2: m = 1 + 3k, k > 3, is not a term, since m > 3(1+3) > 3^2.
This is the complement of the disjunction of A079696 with A239708.
Disregarding the first 3 terms, these are the numbers which are in A008864 but not in A239708. This leads to the following characterization: A number m > 2 is a term, i.e., satisfies digitalSum_b(m) <> b for all b > 1, if and only m is a prime number + 1 and m is not the sum of two distinct powers of 2.
a(6) is the only term such that a(n) = Prime(n) + 1. For n < 6, we have a(n) < Prime(n) + 1, and for n > 6, we have a(n) > Prime(n) + 1.
(End)

Examples

			8 has binary expansion (1,0,0,0) whose digit sum 1 is not 2,
ternary expansion (2,2) whose digit sum 4 is not 3,
quaternary expansion (2,0) whose digit sum 2 is not 4,
5-ary expansion (1,3) whose digit sum 4 is not 5,
6-ary expansion (1,2) whose digit sum 3 is not 6,
7-ary expansion (1,1) whose digit sum 2 is not 7,
8-ary expansion (1,0) whose digit sum 1 is not 8,
and b-ary expansion (8) when b>8 whose digit sum is 8 not b. Therefore, 8 is in the sequence.
3 has binary expansion (1,1) whose digit sum is 2, so 3 is not in the sequence.
From _Hieronymus Fischer_, Apr 10 2014: (Start)
a(10) = 42 (the 13th prime + 1)
a(100) = 618 (the 113th prime + 1)
a(1000) = 8172 (the 1026th prime + 1)
a(10^4) = 105254 (the 10042nd prime + 1)
a(10^5) = 1300464 (the 100056th prime + 1)
a(10^6) = 15486872 (the 1000063th prime + 1)
a(10^7) = 179425944 (the 10000071st prime + 1)
a(10^8) = 2038076324 (the 10^8 +84th prime + 1)
a(10^9) = 22801765334 (the 10^9 +92nd prime + 1)
a(10^10) = 252097803264 (the 10^10 +102nd prime + 1)
[calculation for large numbers processed with Smalltalk method A187813With: estimate; see Prog section]
(End)
		

Crossrefs

Programs

  • Mathematica
    Q@n_:=AllTrue[Table[{b,Plus@@IntegerDigits[n,b]},{b,2,n}],#[[1]]!=#[[2]]&];
    Select[Range[0, 1000], Q] (* Hans Rudolf Widmer, Oct 08 2022 *)
  • Python
    from itertools import count, islice
    from sympy import isprime
    def A187813_gen(startvalue=0): # generator of terms >= startvalue
        yield from filter(lambda n:n<3 or (isprime(n-1) and n.bit_count()!=2), count(max(startvalue,0)))
    A187813_list = list(islice(A187813_gen(startvalue=20),30)) # Chai Wah Wu, Mar 24 2025
  • Sage
    n=1000 #change n for more terms
    S=[]
    for i in [0..n]:
        test=False
        for b in [2..i]:
            if sum(Integer(i).digits(base=b))==b:
                test=True
                break
        if not test:
            S.append(i)
    S
    # From Hieronymus Fischer, Apr 10 2014: (Start)
    
  • Smalltalk
    A187813NextTerm
      "Calculates the next term of A187813 greater than the receiver, i.e., calculates a(n+1) from a(n).
      Usage: a(n) A187813NextTerm
      Answer: a(n+1)
      Version 1: Using numOfBasesWithDigitalSumEQBase from A239703 ==> fast calculation, since only the divisors of  have to tested to be candidates for bases b with base-b digital sum equal to b"
      | an |
      an := self + 1.
      [an numOfBasesWithDigitalSumEQBase > 0]
      whileTrue: [an := an+1].
      ^an
    -----------
    A187813NextTerm
      "Calculates the next term of A187813 greater than the receiver, i.e., calculates a(n+1) from a(n).
      Usage: a(n) A187813NextTerm
      Answer: a(n+1)
      Version 2: Using the equivalence with A008864 and A239708 ==> even much more faster calculation"
      | p q |
      self < 0 ifTrue: [^0].
      self = 0 ifTrue: [^1].
      self = 1 ifTrue: [^2].
      p := (self - 1) nextPrime.
      q := p+1-(2 raisedToInteger: (p+1 integerFloorLog: 2)).
      [q > 0 and: [(2 raisedToInteger: (q integerFloorLog: 2)) - q = 0]] whileTrue: [p := p nextPrime.
                       q := p + 1 - (2 raisedToInteger: (p + 1 integerFloorLog: 2))].
      ^p + 1
    -----------
    A187813
      "Calculates the n-th term of A187813, iteratively.
      Usage: n A187813
      Answer: a(n)"
      | an n |
      n := self.
      n < 3 ifTrue: [^#(0 1) at: n].
      an := 2.
      4 to: n do: [:i |an := an A187813NextTerm].
      ^an
    -----------
    A187813rec
      "Calculates the n-th term of A187813, using the recursive method <A187813With: param>
      Usage: n A187813
      Answer: a(n)"
      self < 3 ifTrue: [^#(0 1) at: self].
      ^self A187813With: self prime
    -----------
    A187813With: estimate
    "Method to calculate the n-th term of A187813 based on the value estimate, recursively. The n-th prime is a adequate estimate. Valid for n > 2.
      Usage: n A187813With: estimate
      Answer: a(n)"
      | x m |
      (x:=((m:= estimate A239708inv)+self-3) prime + 1) = estimate
          ifFalse: [^self A187813With: x].
      (m + 1) A239708 = x
          ifTrue: [^self A187813With: x + 4].
      ^x
    [End]
    

Formula

From Hieronymus Fischer, Mar 27 2014: (Start)
A239703(a(n)) = 0.
a(n+1) = min (p > a(n) | A239703(p) = 0)
[for a Smalltalk implementation see Prog section, method A187813NextTerm version 1].
a(n+1) = 1 + min (p > a(n) | p is prime AND ((q := p+1 - 2^floor(log_2(p+1)) = 0) OR (2^floor(log_2(q)) <> q)))
[for a Smalltalk implementation see Prog section, method A187813NextTerm version 2].
a(n) > Prime(n), for n > 5.
a(n - m) < Prime(n), for n > 1, where m := i*(i-1)/2 + j - 1, i := floor(log_2(Prime(n))), j := floor(log_2(Prime(n) - 2^i)).
a(n - m) < Prime(n), for n > 32, where m := i*(i-1)/2 + j - 16 with i and j above.
a(n) = Prime(n + m - 3) + 1, where m = max ( k | A239708(k) < a(n)), n > 3.
Remark: This identity can be used to calculate a(n) recursively. For a Smalltalk implementation see Prog section, methods A187813rec and A187813With: estimate.
With same conditions: a(n) = A008864(n + m - 3).
a(n - m + 3) = Prime(n) + 1, where m = max ( k | A239708(k) < Prime(n)), n > 3, provided Prime(n) + 1 is not a term of A239708.
(End)

A107579 Primes with digit sum 10.

Original entry on oeis.org

19, 37, 73, 109, 127, 163, 181, 271, 307, 433, 523, 541, 613, 631, 811, 1009, 1063, 1117, 1153, 1171, 1423, 1531, 1621, 1801, 2017, 2053, 2143, 2161, 2251, 2341, 2503, 2521, 3061, 3313, 3331, 3511, 4051, 4231, 5023, 5113, 6121, 6211, 6301, 8011, 8101
Offset: 1

Views

Author

Zak Seidov, May 16 2005

Keywords

Comments

Subset of A061237 and A117674.

Crossrefs

Cf. A000040 (primes), A007953 (sum of digits), A052224 (digit sum = 10).
Cf. A061237 (sum of digits == 1 (mod 9)).
Subsequence of A062340 (primes with digit sum divisible by 5).
Cf. A062339 (same for digit sum s = 4), A062341 (s = 5), A062343 (s = 8), A106754 (s = 11), and others listed in A244918 (s = 68).

Programs

  • Magma
    [p: p in PrimesUpTo(10000) | &+Intseq(p) eq 10]; // Vincenzo Librandi, Jul 08 2014
    
  • Maple
    a:=proc(n) local nn: nn:=convert(n,base,10): if isprime(n)=true and add(nn[j], j=1..nops(nn))=10 then n else end if end proc: seq(a(n),n=1..10^4); # Emeric Deutsch, Mar 06 2008
  • Mathematica
    Select[Prime[Range[100000]], Total[IntegerDigits[#]]==10 &] (* Vincenzo Librandi, Jul 08 2014 *)
  • PARI
    forprime(p=19,8101,if(10==sumdigits(p),print(p","))) \\ Zak Seidov, Oct 08 2016
    
  • PARI
    (A107579_nxt(p)=until(isprime(p=A228915(p)),); p); A107579_first(N=100)=vector(N, i, p=if(i>1, A107579_nxt(p), 19)) \\ M. F. Hasler, Mar 15 2022
    
  • Python
    from itertools import count, islice
    from sympy import isprime
    from sympy.utilities.iterables import multiset_permutations
    def agen(b=10, sod=10): # generator for any base, sum-of-digits
        if 0 <= sod < b:
            yield sod
        nzdigs = [i for i in range(1, b) if i <= sod]
        nzmultiset = []
        for d in range(1, b):
            nzmultiset += [d]*(sod//d)
        for d in count(2):
            fullmultiset = [0]*(d-1-(sod-1)//(b-1)) + nzmultiset
            for firstdig in nzdigs:
                target_sum, restmultiset = sod - int(firstdig), fullmultiset[:]
                restmultiset.remove(firstdig)
                for p in multiset_permutations(restmultiset, d-1):
                    if sum(p) == target_sum:
                        t = int("".join(map(str, [firstdig]+p)), b)
                        if isprime(t):
                            yield t
                        if p[0] == target_sum:
                            break
    print(list(islice(agen(), 45))) # Michael S. Branicky, Mar 10 2022
    
  • Python
    from sympy import isprime
    def A107579(p=19):
        "Return a generator of the sequence of all primes >= p with the same digit sum as p."
        while True:
            if isprime(p): yield p
            p = A228915(p) # skip to next larger integer with the same digit sum
    a=A107579(); [next(a) for  in range(50)] # _M. F. Hasler, Mar 16 2022

Formula

Intersection of A000040 (primes) and A052224 (digit sum = 10). - M. F. Hasler, Mar 09 2022

Extensions

Edited by N. J. A. Sloane, Feb 20 2009 at the suggestion of Pacha Nambi

A226636 Numbers whose base-3 sum of digits is 3.

Original entry on oeis.org

5, 7, 11, 13, 15, 19, 21, 29, 31, 33, 37, 39, 45, 55, 57, 63, 83, 85, 87, 91, 93, 99, 109, 111, 117, 135, 163, 165, 171, 189, 245, 247, 249, 253, 255, 261, 271, 273, 279, 297, 325, 327, 333, 351, 405, 487, 489, 495, 513, 567, 731, 733, 735, 739, 741, 747, 757
Offset: 1

Views

Author

Tom Edgar, Aug 31 2013

Keywords

Comments

All of the entries are odd.
Subsequence of A005408. - Michel Marcus, Sep 03 2013
In general, the set of numbers with sum of base-b digits equal to b is a subset of { (b-1)*k + 1; k = 2, 3, 4, ... }. - M. F. Hasler, Dec 23 2016

Examples

			The ternary expansion of 5 is (1,2), which has sum of digits 3.
The ternary expansion of 31 is (1,0,0,2), which has sum of digits 3.
10 is not on the list since the ternary expansion of 10 is (1,0,1), which has sum of digits 2 not 3.
		

Crossrefs

Cf. A226969 (b = 4), A227062 (b = 5), A227080 (b = 6), A227092 (b = 7), A227095 (b = 8), A227238 (b = 9), A052224 (b = 10).

Programs

  • Maple
    N:= 10: # for all terms < 3^(N+1)
    [seq(seq(seq(3^a+3^b+3^c, c=0..`if`(b=a, b-1,b)),b = 0..a),a=0..N)]; # Robert Israel, Jun 05 2018
  • Mathematica
    Select[Range@ 757, Total@ IntegerDigits[#, 3] == 3 &] (* Michael De Vlieger, Dec 23 2016 *)
  • PARI
    select( is(n)=sumdigits(n,3)==3, [1..999]) \\ M. F. Hasler, Dec 23 2016
    
  • Python
    from itertools import islice
    def nextsod(n, base):
        c, b, w = 0, base, 0
        while True:
            d = n%b
            if d+1 < b and c:
                return (n+1)*b**w + ((c-1)%(b-1)+1)*b**((c-1)//(b-1))-1
            c += d; n //= b; w += 1
    def A226636gen(sod=3, base=3): # generator of terms for any sod, base
        an = (sod%(base-1)+1)*base**(sod//(base-1))-1
        while True: yield an; an = nextsod(an, base)
    print(list(islice(A226636gen(), 57))) # Michael S. Branicky, Jul 10 2022, generalizing the code by M. F. Hasler in A052224
  • Sage
    [i for i in [0..1000] if sum(Integer(i).digits(base=3))==3]
    

Formula

a(k^3/6 + k^2 + 5*k/6 + j) = 3^(k+1) + A055235(j-1) for 1 <= j <= k^2/2+5*k/2+2. - Robert Israel, Jun 05 2018

A279769 Numbers n such that the sum of digits of 9n is 18.

Original entry on oeis.org

11, 21, 22, 31, 32, 33, 41, 42, 43, 44, 51, 52, 53, 54, 55, 61, 62, 63, 64, 65, 66, 71, 72, 73, 74, 75, 76, 77, 81, 82, 83, 84, 85, 86, 87, 88, 91, 92, 93, 94, 95, 96, 97, 98, 99, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 121, 122, 131, 132, 133, 141
Offset: 1

Views

Author

M. F. Hasler, Dec 18 2016

Keywords

Comments

Differs from A084854 from a(55) = 110 on.
Numbers n such that A008591(n) is a term of A235228. - Felix Fröhlich, Dec 18 2016
The digital sum of 9n is always a multiple of 9, and never zero. For most numbers < 100, the digital sum is equal to 9, but for example in the range [91..110] all numbers except 100 have their digital sum equal to 18. The b-file / graph gives a hint on the "asymptotic" distribution / density of this set. After a "flat" range like that at [91..110] there comes a record gap. Sizes [and upper ends] of record gaps are: 10 [a(2) = 21], 11 [a(56) = 121, a(119) = 231, a(188) = 341, ..., a(553) = 891, a(616) = 1001], 21 [a(671) = 1121], 31 [a(1331) = 2231], ..., 91 [a(4339) = 8891], 101 [a(4621) = 10001], 121 [a(4841) = 11121], 231 [a(9176) = 22231], ..., 891 [a(24217) = 88891], 1001 [a(25213) = 100001], 1121 [a(25928) = 111121], 2231 [a(47510) = 222231], ..., 8891 [a(108577) = 888891], 10001 [a(111574) = 1000001], 11121 [a(113576) = 1111121], 22231 [a(202511) = 2222231], ..., 88891 [a(416215) = 8888891], ... - M. F. Hasler, Dec 22 2016

Crossrefs

Cf. A007953 (digital sum), A008591, A084854.
Cf. A279772 (sumdigits(2n) = 4), A279773 (sumdigits(3n) = 6), A279774 (sumdigits(4n) = 8), A279775 (sumdigits(5n) = 10), A279776 (sumdigits(6n) = 12), A279770 (sumdigits(7n) = 14), A279768 (sumdigits(8n) = 16), A279769 (sumdigits(9n) = 18), A279777 (sumdigits(9n) = 27).
Digital sum of m*n equals m: A088404 = A069537/2, A088405 = A052217/3, A088406 = A063997/4, A088407 = A069540/5, A088408 = A062768/6, A088409 = A063416/7, A088410 = A069543/8.
Cf. A005349 (Niven or Harshad numbers), A245062 (arranged in rows by digit sums).
Numbers with given digital sum: A011557 (1), A052216 (2), A052217 (3), A052218 (4), A052219 (5), A052220 (6), A052221 (7), A052222 (8), A052223 (9), A052224 (10), A166311 (11), A235151 (12), A143164 (13), A235225 (14), A235226 (15), A235227 (16), A166370 (17), A235228 (18), A166459 (19), A235229 (20).

Programs

  • Mathematica
    Select[Range@ 141, Total@ IntegerDigits[9 #] == 18 &]
  • PARI
    is(n) = sumdigits(9*n)==18 \\ Felix Fröhlich, Dec 18 2016

Formula

a(n) = A235228(n)/9.

A227062 Numbers whose base-5 sum of digits is 5.

Original entry on oeis.org

9, 13, 17, 21, 29, 33, 37, 41, 45, 53, 57, 61, 65, 77, 81, 85, 101, 105, 129, 133, 137, 141, 145, 153, 157, 161, 165, 177, 181, 185, 201, 205, 225, 253, 257, 261, 265, 277, 281, 285, 301, 305, 325, 377, 381, 385, 401, 405, 425, 501, 505, 525, 629, 633, 637
Offset: 1

Views

Author

Tom Edgar, Sep 01 2013

Keywords

Comments

All of the entries are odd.
Subsequence of A016813. - Michel Marcus, Sep 03 2013
In general, the set of numbers with sum of base-b digits equal to b is a subset of { (b-1)*k + 1; k = 2, 3, 4, ... }. - M. F. Hasler, Dec 23 2016

Examples

			The 5-ary expansion of 9 is (1,4), which has sum of digits 5.
The 5-ary expansion of 53 is (2,0,3), which has sum of digits 5.
10 is not on the list since the 5-ary expansion of 10 is (2,0), which has sum of digits 2 not 5.
		

Crossrefs

Cf. A226636 (b = 3), A226969 (b = 4), A227080 (b = 6), A227092 (b = 7), A227095 (b = 8), A227238 (b = 9), A052224 (b = 10).

Programs

  • Mathematica
    Select[Range@ 640, Total@ IntegerDigits[#, 5] == 5 &] (* Michael De Vlieger, Dec 23 2016 *)
  • PARI
    select( is(n)=sumdigits(n,5)==5, [1..999]) \\ M. F. Hasler, Dec 23 2016
    
  • Python
    from sympy.utilities.iterables import multiset_permutations
    def auptodigs(maxdigits_base5):
        alst = []
        for d in range(2, maxdigits_base5 + 1):
            fulldigset = list("0"*(d-2) + "111112234")
            for firstdig in "1234":
                target_sum, restdigset = 5 - int(firstdig), fulldigset[:]
                restdigset.remove(firstdig)
                for p in multiset_permutations(restdigset, d-1):
                    if sum(map(int, p)) == target_sum:
                      alst.append(int(firstdig+"".join(p), 5))
                      if int(p[0]) == target_sum:
                          break
        return alst
    print(auptodigs(5)) # Michael S. Branicky, Sep 13 2021
    
  • Python
    agen = A226636gen(sod=5, base=5) # generator of terms using code in A226636
    print([next(agen) for n in range(1, 56)]) # Michael S. Branicky, Jul 10 2022
  • Sage
    [i for i in [0..1000] if sum(Integer(i).digits(base=5))==5]
    

A227080 Numbers whose base-6 sum of digits is 6.

Original entry on oeis.org

11, 16, 21, 26, 31, 41, 46, 51, 56, 61, 66, 76, 81, 86, 91, 96, 111, 116, 121, 126, 146, 151, 156, 181, 186, 221, 226, 231, 236, 241, 246, 256, 261, 266, 271, 276, 291, 296, 301, 306, 326, 331, 336, 361, 366, 396, 436, 441, 446, 451, 456, 471, 476, 481, 486
Offset: 1

Views

Author

Tom Edgar, Sep 01 2013

Keywords

Comments

Subsequence of A016861. - Michel Marcus, Sep 03 2013
In general, the set of numbers with sum of base-b digits equal to b is a subset of { (b-1)*k + 1; k = 2, 3, 4, ... }. - M. F. Hasler, Dec 23 2016

Examples

			The 6-ary expansion of 11 is (1,5), which has sum of digits 6.
The 6-ary expansion of 46 is (1,1,4), which has sum of digits 6.
9 is not on the list since the 6-ary expansion of 10 is (1,3), which has sum of digits 4 not 6.
		

Crossrefs

Cf. A226636 (b = 3), A226639 (b = 4), A227062 (b = 5), A227080 (b = 6), A227092 (b = 7), A227095 (b = 8), A227238 (b = 9), A052224 (b = 10).

Programs

  • Mathematica
    Select[Range[500],Total[IntegerDigits[#,6]]==6&] (* Harvey P. Dale, Nov 25 2016 *)
  • PARI
    select( is(n)=sumdigits(n,6)==6, [1..999]) \\ M. F. Hasler, Dec 23 2016
    
  • Python
    # see A052224 for a faster version if going to high numbers
    from sympy.ntheory import digits
    def ok(n): return sum(digits(n, 6)[1:]) == 6
    print([k for k in range(487) if ok(k)]) # Michael S. Branicky, Nov 16 2021
    
  • Python
    agen = A226636gen(sod=6, base=6) # generator of terms using code in A226636
    print([next(agen) for n in range(1, 56)]) # Michael S. Branicky, Jul 10 2022
  • Sage
    [i for i in [0..1000] if sum(Integer(i).digits(base=6))==6]
    

A279777 Numbers k such that the sum of digits of 9k is 27.

Original entry on oeis.org

111, 211, 221, 222, 311, 321, 322, 331, 332, 333, 411, 421, 422, 431, 432, 433, 441, 442, 443, 444, 511, 521, 522, 531, 532, 533, 541, 542, 543, 544, 551, 552, 553, 554, 555, 611, 621, 622, 631, 632, 633, 641, 642, 643, 644, 651, 652, 653, 654, 655, 661
Offset: 1

Views

Author

M. F. Hasler, Dec 23 2016

Keywords

Comments

The digital sum of 9k is always a multiple of 9. For most numbers below 100 it is actually equal to 9. Numbers such that the digital sum of 9k is 18 are listed in A279769. Only every third term of the present sequence is divisible by 3.
The sequence of record gaps [and upper end of the gap] is: 100 [a(2) = 211], 101 [a(221) = 1211], 111 [a(4841) = 11211], 111 [a(10121) = 22311], 111 [a(15752) = 33411], ..., 111 [a(45133) = 88911], 111 [a(50413) = 100011], 211 [a(55253) = 111211], 311 [a(110000) = 222311], ..., 911 [a(380557) = 888911], 1011 [a(411049) = 1000011], 1211 [a(436976) = 1111211], 2311 [a(840281) = 2222311], ..., 8911 [a(2451241) = 8888911], ...

Crossrefs

Cf. A008591, A084854, A003991, A004247, A279769 (sumdigits(9n) = 18).
Digital sum of m*n equals m: A088404 = A069537/2, A088405 = A052217/3, A088406 = A063997/4, A088407 = A069540/5, A088408 = A062768/6, A088409 = A063416/7, A088410 = A069543/8.
Numbers with given digital sum: A011557 (1), A052216 (2), A052217 (3), A052218 (4), A052219 (5), A052220 (6), A052221 (7), A052222 (8), A052223 (9), A052224 (10), A166311 (11), A235151 (12), A143164 (13), A235225 (14), A235226 (15), A235227 (16), A166370 (17), A235228 (18), A166459 (19), A235229 (20).
Cf. A007953 (digital sum), A005349 (Niven or Harshad numbers), A245062 (arranged in rows by digit sums).
Cf. A082259.

Programs

  • Mathematica
    Select[Range@ 661, Total@ IntegerDigits[9 #] == 27 &] (* Michael De Vlieger, Dec 23 2016 *)
  • PARI
    is(n)=sumdigits(9*n)==27

A226969 Numbers whose base-4 sum of digits is 4.

Original entry on oeis.org

7, 10, 13, 19, 22, 25, 28, 34, 37, 40, 49, 52, 67, 70, 73, 76, 82, 85, 88, 97, 100, 112, 130, 133, 136, 145, 148, 160, 193, 196, 208, 259, 262, 265, 268, 274, 277, 280, 289, 292, 304, 322, 325, 328, 337, 340, 352, 385, 388, 400, 448, 514, 517, 520, 529, 532
Offset: 1

Views

Author

Tom Edgar, Sep 01 2013

Keywords

Comments

Subsequence of A016777. - Michel Marcus, Sep 03 2013
In general, the set of numbers with sum of base-b digits equal to b is a subset of { (b-1)*k + 1; k = 2, 3, 4, ... }. - M. F. Hasler, Dec 23 2016

Examples

			The quaternary expansion of 13 is (3,1), which has sum of digits 4.
The quaternary expansion of 40 is (2,2,0), which has sum of digits 4.
17 is not on the list since the quaternary expansion of 17 is (1,0,1), which has sum of digits 2 not 4.
		

Crossrefs

Cf. A226636 (b = 3), A227062 (b = 5), A227080 (b = 6), A227092 (b = 7), A227095 (b = 8), A227238 (b = 9), A052224 (b = 10).

Programs

  • Mathematica
    Select[Range@ 540, Total@ IntegerDigits[#, 4] == 4 &] (* Michael De Vlieger, Dec 23 2016 *)
  • PARI
    select( is(n)=sumdigits(n,4)==4, [1..999]) \\ M. F. Hasler, Dec 23 2016
    
  • Python
    agen = A226636gen(sod=4, base=4) # generator of terms using code in A226636
    print([next(agen) for n in range(1, 57)]) # Michael S. Branicky, Jul 10 2022
  • Sage
    [i for i in [0..1000] if sum(Integer(i).digits(base=4))==4]
    

A227092 Numbers whose base-7 sum of digits is 7.

Original entry on oeis.org

13, 19, 25, 31, 37, 43, 55, 61, 67, 73, 79, 85, 91, 103, 109, 115, 121, 127, 133, 151, 157, 163, 169, 175, 199, 205, 211, 217, 247, 253, 259, 295, 301, 349, 355, 361, 367, 373, 379, 385, 397, 403, 409, 415, 421, 427, 445, 451, 457, 463, 469, 493, 499, 505
Offset: 1

Views

Author

Tom Edgar, Sep 01 2013

Keywords

Comments

All of the entries are odd.
Subsequence of A016921. - Michel Marcus, Sep 03 2013
In general, the set of numbers with sum of base-b digits equal to b is a subset of { (b-1)*k + 1; k = 2, 3, 4, ... }. - M. F. Hasler, Dec 23 2016

Examples

			The 7-ary expansion of 13 is (1,6), which has sum of digits 7.
The 7-ary expansion of 103 is (2,0,5), which has sum of digits 7.
10 is not on the list since the 7-ary expansion of 10 is (1,3), which has sum of digits 4 not 7.
		

Crossrefs

Cf. A226636 (b = 3), A226969 (b = 4), A227062 (b = 5), A227080 (b = 6), A227092 (b = 7), A227095 (b = 8), A227238 (b = 9), A052224 (b = 10).

Programs

  • Mathematica
    Select[Range[600],Total[IntegerDigits[#,7]]==7&] (* Harvey P. Dale, Aug 18 2014 *)
  • PARI
    select( is(n)=sumdigits(n,7)==7, [1..999]) \\ M. F. Hasler, Dec 23 2016
    
  • Python
    agen = A226636gen(sod=7, base=7) # generator of terms using code in A226636
    print([next(agen) for n in range(1, 55)]) # Michael S. Branicky, Jul 10 2022
  • Sage
    [i for i in [0..1000] if sum(Integer(i).digits(base=7))==7]
    
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