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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A005823 Numbers whose ternary expansion contains no 1's.

Original entry on oeis.org

0, 2, 6, 8, 18, 20, 24, 26, 54, 56, 60, 62, 72, 74, 78, 80, 162, 164, 168, 170, 180, 182, 186, 188, 216, 218, 222, 224, 234, 236, 240, 242, 486, 488, 492, 494, 504, 506, 510, 512, 540, 542, 546, 548, 558, 560, 564, 566, 648, 650, 654, 656, 666, 668, 672, 674
Offset: 1

Views

Author

Keywords

Comments

The set of real numbers between 0 and 1 that contain no 1's in their ternary expansion is the well-known Cantor set with Hausdorff dimension log 2 / log 3.
Complement of A081606. - Reinhard Zumkeller, Mar 23 2003
Numbers k such that the k-th Apery number is congruent to 1 (mod 3) (cf. A005258). - Benoit Cloitre, Nov 30 2003
Numbers k such that the k-th central Delannoy number is congruent to 1 (mod 3) (cf. A001850). - Benoit Cloitre, Nov 30 2003
Numbers k such that there exists a permutation p_1, ..., p_k of 1, ..., k such that i + p_i is a power of 3 for every i. - Ray Chandler, Aug 03 2004
Subsequence of A125292. - Reinhard Zumkeller, Nov 26 2006
The first 2^n terms of the sequence could be obtained using the Cantor process for the segment [0,3^n-1]. E.g., for n=2 we have [0,{1},2,{3,4,5},6,{7},8]. The numbers outside of braces are the first 4 terms of the sequence. Therefore the terms of the sequence could be called "Cantor's numbers". - Vladimir Shevelev, Jun 13 2008
Mahler proved that positive a(n) is never a square. - Michel Marcus, Nov 12 2012
Define t: Z -> P(R) so that t(k) is the translated Cantor ternary set spanning [k, k+1], and let T be the union of t(a(n)) for all n. T = T * 3 = T / 3 is the closure of the Cantor ternary set under multiplication by 3. - Peter Munn, Oct 30 2019

References

  • K. J. Falconer, The Geometry of Fractal Sets, Cambridge, 1985; p. 14.
  • N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Crossrefs

Twice A005836.
Cf. A088917 (characteristic function), A306556.

Programs

  • Maple
    a:= proc(n) option remember;
          `if`(n=1, 0, `if`(irem (n, 2, 'q')=0, 3*a(q)+2, 3*a(q+1)))
        end:
    seq(a(n), n=1..100); # Alois P. Heinz, Apr 19 2012
  • Mathematica
    Select[ Range[ 0, 729 ], (Count[ IntegerDigits[ #, 3 ], 1 ]==0)& ]
    Select[Range[0,700],DigitCount[#,3,1]==0&] (* Harvey P. Dale, Mar 12 2016 *)
  • PARI
    is(n)=while(n,if(n%3==1,return(0),n\=3));1 \\ Charles R Greathouse IV, Apr 20 2012
    
  • PARI
    a(n)=n=binary(n-1);sum(i=1,#n,2*n[i]*3^(#n-i)) \\ Charles R Greathouse IV, Apr 20 2012
    
  • PARI
    a(n)=2*fromdigits(binary(n-1),3) \\ Charles R Greathouse IV, Aug 24 2016
    
  • Python
    def A005823(n):
        return 2*int(format(n-1,'b'),3) # Chai Wah Wu, Jan 04 2015

Formula

a(n) = 2 * A005836(n).
a(2n) = 3*a(n)+2, a(2n+1) = 3*a(n+1), a(1) = 0.
a(n) = Sum_{k = 1..n} 1 + 3^A007814(k). - Philippe Deléham, Jul 09 2005
A125291(a(n)) = 1 for n>0. - Reinhard Zumkeller, Nov 26 2006
From Reinhard Zumkeller, Mar 02 2008: (Start)
A062756(a(n)) = 0.
If the offset were changed to zero, then: a(0) = 0, a(n+1) = f(a(n)+1, a(n)+1) where f(x, y) = if x < 3 and x <> 1 then y else if x mod 3 = 1 then f(y+1, y+1) else f(floor(x/3), y). (End)
G.f. g(x) satisfies g(x) = 3*g(x^2)*(1+1/x) + 2*x^2/(1-x^2). - Robert Israel, Jan 04 2015
Sum_{n>=2} 1/a(n) = 1.341426555483087715426958452292349687410838545707857407585878304836140592352... (calculated using Baillie and Schmelzer's kempnerSums.nb, see Links). - Amiram Eldar, Feb 12 2022

Extensions

More terms from Sascha Kurz, Mar 24 2002
Offset corrected by N. J. A. Sloane, Mar 02 2008. This may require some of the formulas to be adjusted.

A077267 Number of zeros in base-3 expansion of n.

Original entry on oeis.org

1, 0, 0, 1, 0, 0, 1, 0, 0, 2, 1, 1, 1, 0, 0, 1, 0, 0, 2, 1, 1, 1, 0, 0, 1, 0, 0, 3, 2, 2, 2, 1, 1, 2, 1, 1, 2, 1, 1, 1, 0, 0, 1, 0, 0, 2, 1, 1, 1, 0, 0, 1, 0, 0, 3, 2, 2, 2, 1, 1, 2, 1, 1, 2, 1, 1, 1, 0, 0, 1, 0, 0, 2, 1, 1, 1, 0, 0, 1, 0, 0, 4, 3, 3, 3, 2, 2, 3, 2, 2, 3, 2, 2, 2, 1, 1, 2, 1, 1, 3, 2, 2, 2, 1, 1, 2
Offset: 0

Views

Author

Henry Bottomley, Nov 01 2002

Keywords

Examples

			a(8)=0 since 8 written in base 3 is 22 with 0 zeros;
a(9)=2 since 9 written in base 3 is 100 with 2 zeros;
a(10)=1 since 10 written in base 3 is 101 with 1 zero.
		

Crossrefs

Programs

Formula

a(1)=a(2)=0; a(3n)=a(n)+1; a(3n+1)=a(3n+2)=a(n). a(3^n-2)=a(3^n-1)=0; a(3^n)=n. a(n)=A077266(n, 3).
a(n) + A062756(n) + A081603(n) = A081604(n). - Reinhard Zumkeller, Mar 23 2003
G.f.: (Sum_{k>=0} x^(3^(k+1))/(1 + x^(3^k) + x^(2*3^k)))/(1-x). - Franklin T. Adams-Watters, Nov 03 2005
a(n) = A079978(n) if n < 3, A079978(n) + a(floor(n/3)) otherwise. - Reinhard Zumkeller, Feb 21 2013

Extensions

a(0)=1 added, offset changed to 0 and b-file adjusted by Reinhard Zumkeller, Feb 21 2013
Wrong formula deleted by Reinhard Zumkeller, Feb 21 2013

A023705 Numbers with no 0's in base-4 expansion.

Original entry on oeis.org

1, 2, 3, 5, 6, 7, 9, 10, 11, 13, 14, 15, 21, 22, 23, 25, 26, 27, 29, 30, 31, 37, 38, 39, 41, 42, 43, 45, 46, 47, 53, 54, 55, 57, 58, 59, 61, 62, 63, 85, 86, 87, 89, 90, 91, 93, 94, 95, 101, 102, 103, 105, 106, 107, 109, 110, 111, 117, 118, 119, 121, 122, 123
Offset: 1

Views

Author

Keywords

Comments

A032925 is the intersection of this sequence and A023717; cf. A179888. - Reinhard Zumkeller, Jul 31 2010

Crossrefs

Zeroless numbers in some other bases <= 10: A000042 (base 2), A032924 (base 3), A248910 (base 6), A255805 (base 8), A255808 (base 9), A052382 (base 10).
Cf. A100968 (subsequence).

Programs

  • C
    #include 
    uint32_t a_next(uint32_t a_n) { return (a_n + 1) | ((a_n & (a_n + 0xaaaaaaab)) >> 1); } /* Falk Hüffner, Jan 22 2022 */
    
  • Haskell
    a023705 n = a023705_list !! (n-1)
    a023705_list = iterate f 1 where
       f x = 1 + if r < 3 then x else 4 * f x'
             where (x', r) = divMod x 4
    -- Reinhard Zumkeller, Mar 06 2015, Oct 19 2011
    
  • Magma
    [n: n in [1..130] | not 0 in Intseq(n,4)]; // Vincenzo Librandi, Oct 04 2018
    
  • Maple
    R:= [1,2,3]: A:= 1,2,3:
    for i from 1 to 4 do
      R:= map(t -> (4*t+1,4*t+2,4*t+3), R);
      A:= A, op(R);
    od:
    A; # Robert Israel, Oct 04 2018
  • Mathematica
    Select[ Range[ 120 ], (Count[ IntegerDigits[ #, 4 ], 0 ]==0)& ]
    Select[Range[200],DigitCount[#,4,0]==0&] (* Harvey P. Dale, Dec 23 2015 *)
  • PARI
    isok(n) = vecmin(digits(n, 4)); \\ Michel Marcus, Jul 04 2015
    
  • Python
    from sympy import integer_log
    def A023705(n):
        m = integer_log(k:=(n<<1)+1,3)[0]
        return sum(1+(k-3**m)//(3**j<<1)%3<<(j<<1) for j in range(m)) # Chai Wah Wu, Jun 27 2025

Formula

G.f. g(x) satisfies g(x) = (x+2*x^2+3*x^3)/(1-x^3) + 4*(x+x^2+x^3)*g(x^3). - Robert Israel, Oct 04 2018

A081605 Numbers having at least one 0 in their ternary representation.

Original entry on oeis.org

0, 3, 6, 9, 10, 11, 12, 15, 18, 19, 20, 21, 24, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 42, 45, 46, 47, 48, 51, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 69, 72, 73, 74, 75, 78, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100
Offset: 1

Views

Author

Reinhard Zumkeller, Mar 23 2003

Keywords

Comments

Complement of A032924.
A212193(a(n)) <> 0. [Reinhard Zumkeller, May 04 2012]

Crossrefs

Programs

  • Haskell
    import Data.List (findIndices)
    a081605 n = a081605_list !! (n-1)
    a081605_list = findIndices (/= 0) a212193_list
    -- Reinhard Zumkeller, May 04 2012
    
  • Mathematica
    Select[Range[0,100],DigitCount[#,3,0]>0&] (* Harvey P. Dale, Aug 10 2021 *)
  • Python
    from itertools import count, islice
    def A081605_gen(): # generator of terms
        a = -1
        for n in count(2):
            b = int(bin(n)[3:],3) + (3**(n.bit_length()-1)-1>>1)
            yield from range(a+1,b)
            a = b
    A081605_list = list(islice(A081605_gen(),30)) # Chai Wah Wu, Oct 13 2023

A255805 Numbers with no zeros in base-8 representation.

Original entry on oeis.org

1, 2, 3, 4, 5, 6, 7, 9, 10, 11, 12, 13, 14, 15, 17, 18, 19, 20, 21, 22, 23, 25, 26, 27, 28, 29, 30, 31, 33, 34, 35, 36, 37, 38, 39, 41, 42, 43, 44, 45, 46, 47, 49, 50, 51, 52, 53, 54, 55, 57, 58, 59, 60, 61, 62, 63, 73, 74, 75, 76, 77, 78, 79, 81, 82, 83, 84
Offset: 1

Views

Author

Reinhard Zumkeller, Mar 08 2015

Keywords

Comments

Different from A047592, A207481.

Crossrefs

Cf. A007094, A100970 (subsequence).
Zeroless numbers in some other bases <= 10: A000042 (base 2), A032924 (base 3), A023705 (base 4), A248910 (base 6), A255808 (base 9), A052382 (base 10).

Programs

  • Haskell
    a255805 n = a255805_list !! (n-1)
    a255805_list = iterate f 1 where
       f x = 1 + if r < 7 then x else 8 * f x'  where (x', r) = divMod x 8
    
  • Mathematica
    Select[Range[100],DigitCount[#,8,0]==0&] (* Harvey P. Dale, Jun 08 2015 *)
  • PARI
    isok(m) = vecmin(digits(m,8)) > 0; \\ Michel Marcus, Jan 23 2022
    
  • Python
    def ok(n): return '0' not in oct(n)[2:]
    print([k for k in range(85) if ok(k)]) # Michael S. Branicky, Jan 23 2022
    
  • Python
    from sympy import integer_log
    def A255805(n):
        m = integer_log(k:=6*n+1,7)[0]
        return sum(1+(k-7**m)//(6*7**j)%7<<3*j for j in range(m)) # Chai Wah Wu, Jun 28 2025

A248910 Numbers with no zeros in base-6 representation.

Original entry on oeis.org

1, 2, 3, 4, 5, 7, 8, 9, 10, 11, 13, 14, 15, 16, 17, 19, 20, 21, 22, 23, 25, 26, 27, 28, 29, 31, 32, 33, 34, 35, 43, 44, 45, 46, 47, 49, 50, 51, 52, 53, 55, 56, 57, 58, 59, 61, 62, 63, 64, 65, 67, 68, 69, 70, 71, 79, 80, 81, 82, 83, 85, 86, 87, 88, 89, 91, 92
Offset: 1

Views

Author

Reinhard Zumkeller, Mar 08 2015

Keywords

Comments

Different from A039215, A047253, A184522, A187390, A194386.

Crossrefs

Cf. A007092, A100969 (subsequence).
Zeroless numbers in some other bases <= 10: A000042 (base 2), A032924 (base 3), A023705 (base 4), A255805 (base 8), A255808 (base 9), A052382 (base 10).

Programs

  • Haskell
    a248910 n = a248910_list !! (n-1)
    a248910_list = iterate f 1 where
       f x = 1 + if r < 5 then x else 6 * f x'  where (x', r) = divMod x 6
    
  • Mathematica
    Select[Range[100], DigitCount[#,6, 0] == 0 &] (* Paolo Xausa, Jun 29 2025 *)
  • PARI
    isok(m) = vecmin(digits(m, 6)) > 0; \\ Michel Marcus, Jan 23 2022
    
  • Python
    from sympy import integer_log
    def A248910(n):
        m = integer_log(k:=(n<<2)+1,5)[0]
        return sum((1+(k-5**m)//(5**j<<2)%5)*6**j for j in range(m)) # Chai Wah Wu, Jun 28 2025

A255808 Numbers with no zeros in base-9 representation.

Original entry on oeis.org

1, 2, 3, 4, 5, 6, 7, 8, 10, 11, 12, 13, 14, 15, 16, 17, 19, 20, 21, 22, 23, 24, 25, 26, 28, 29, 30, 31, 32, 33, 34, 35, 37, 38, 39, 40, 41, 42, 43, 44, 46, 47, 48, 49, 50, 51, 52, 53, 55, 56, 57, 58, 59, 60, 61, 62, 64, 65, 66, 67, 68, 69, 70, 71, 73, 74, 75
Offset: 1

Views

Author

Reinhard Zumkeller, Mar 08 2015

Keywords

Comments

a(n) = A168183(n) for n <= 72.

Crossrefs

Cf. A007095, A100973 (subsequence).
Zeroless numbers in some other bases <= 10: A000042 (base 2), A032924 (base 3), A023705 (base 4), A248910 (base 6), A255805 (base 8), A052382 (base 10).

Programs

  • Haskell
    a255808 n = a255808_list !! (n-1)
    a255808_list = iterate f 1 where
       f x = 1 + if r < 8 then x else 9 * f x'  where (x', r) = divMod x 9
    
  • Mathematica
    Select[Range[100],DigitCount[#,9,0]==0&] (* or *) With[{upto=100}, Complement[ Range[upto],9*Range[Floor[upto/9]]]] (* Harvey P. Dale, May 29 2019 *)
  • PARI
    isok(n) = vecmin(digits(n, 9)) != 0; \\ Michel Marcus, Jun 29 2019
    
  • Python
    def A255808(n):
        m = ((k:=7*n+1).bit_length()-1)//3
        return sum((1+((k-(1<<3*m))//(7<<3*j)&7))*9**j for j in range(m)) # Chai Wah Wu, Jun 28 2025

A154314 Numbers with not more than two distinct digits in ternary representation.

Original entry on oeis.org

0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 13, 14, 16, 17, 18, 20, 22, 23, 24, 25, 26, 27, 28, 30, 31, 36, 37, 39, 40, 41, 43, 44, 49, 50, 52, 53, 54, 56, 60, 62, 67, 68, 70, 71, 72, 74, 76, 77, 78, 79, 80, 81, 82, 84, 85, 90, 91, 93, 94, 108, 109, 111, 112, 117, 118, 120, 121, 122
Offset: 1

Views

Author

Reinhard Zumkeller, Jan 07 2009

Keywords

Crossrefs

Complement of A031944.
Union of A032924, A005823 and A005836.

Programs

  • Haskell
    import Data.List (findIndices)
    a154314 n = a154314_list !! (n-1)
    a154314_list = findIndices (/= 3) a212193_list
    -- Reinhard Zumkeller, May 04 2012
    
  • Mathematica
    Select[Range[0,200],Length[Union[IntegerDigits[#,3]]]<3&] (* Harvey P. Dale, Nov 23 2012 *)
  • PARI
    is(n)=#Set(digits(n,3))<3 \\ Charles R Greathouse IV, Mar 17 2014

Formula

A043530(a(n)) <= 2.
A212193(a(n)) <> 3. - Reinhard Zumkeller, May 04 2012
a(n) >> n^1.58..., where the exponent is log(3)/log(2). - Charles R Greathouse IV, Mar 17 2014
Sum_{n>=2} 1/a(n) = 5.47555542241781419692840472181029603722178623821762258873485212626135391726959422416350447132335696748507... (calculated using Baillie and Schmelzer's kempnerSums.nb, see Links). - Amiram Eldar, Apr 14 2025

A059852 Consider the English alphabet in Morse code (the International Morse radio telegraph code). Map a 'dit' to the digit one and a 'dah' to the digit 2, then express that ternary number in decimal.

Original entry on oeis.org

5, 67, 70, 22, 1, 43, 25, 40, 4, 53, 23, 49, 8, 7, 26, 52, 77, 16, 13, 2, 14, 41, 17, 68, 71, 76
Offset: 1

Views

Author

Robert G. Wilson v, Feb 27 2001

Keywords

Comments

Written in base 3, the terms read (12, 2111, 2121, 211, 1, 1121, 221, 1111, 11, 1222, 212, 1211, 22, 21, 222, 1221, 2212, 121, 111, 2, 112, 1112, 122, 2112, 2122, 2211). This contains all words over {1,2} with 1 to 4 letters except for 1122, 1212, 2221 and 2222, which correspond to the codes for Ü, Ä, Ö and CH. - M. F. Hasler, Jun 22 2020

Examples

			The sixth letter, F, is ".._." in Morse. This becomes 1121 in ternary and 43 in decimal, so a(6) = 43.
		

References

  • "Learning the Radiotelegraph Code," Seventh Edition, published by American Radio Relay League, West Hartford 7, Connecticut, 1955.
  • "Morse Code Course," Jeppesen and Company, Denver, Colorado, 1962.
  • "International Morse Code," prepared by Lt. Commander F.R.L. Tuthill, USNR and Lt. (J.G.) E.L. Battey, USNR, published by Insuline Corporation of America, Long Island City, NY.

Crossrefs

Cf. A060110, the same for numbers, and A060109, written in base 3.
Cf. A008777 (number of base 3 digits = dots and dashes in the n-th letter), A281015, A281017, A281018.
Cf. A105386, A105387 (ambiguous variants using digits 0 and 1).

Programs

  • PARI
    A059852=digits(3008707498660932665486381130661318784490079420090,81) \\ or vecextract(apply(A032924,[1..28]), i) with i=numtoperm(26, 58849338891424664724588744) or i=vecsort(Vec("ETIANMSURWDKGOHVFuLaPJBXCYZQ"),,1)[1..26]. - M. F. Hasler, Jun 22 2020

Extensions

Edited, links and crossrefs added by M. F. Hasler, Jun 22 2020

A212193 In ternary representation of n: a(n) = if n is pandigital then 3 else least digit not used.

Original entry on oeis.org

1, 0, 0, 2, 0, 0, 1, 0, 0, 2, 2, 3, 2, 0, 0, 3, 0, 0, 1, 3, 1, 3, 0, 0, 1, 0, 0, 2, 2, 3, 2, 2, 3, 3, 3, 3, 2, 2, 3, 2, 0, 0, 3, 0, 0, 3, 3, 3, 3, 0, 0, 3, 0, 0, 1, 3, 1, 3, 3, 3, 1, 3, 1, 3, 3, 3, 3, 0, 0, 3, 0, 0, 1, 3, 1, 3, 0, 0, 1, 0, 0, 2, 2, 3, 2, 2
Offset: 0

Views

Author

Reinhard Zumkeller, May 04 2012

Keywords

Comments

a(A032924(n)) = 0; a(A081605(n)) <> 0;
a(A031944(n)) = 3; a(A154314(n)) <> 3.

Examples

			.   0 ->   '0':   a(0) = 1
.   1 ->   '1':   a(1) = 0
.   2 ->   '2':   a(2) = 0
.   3 ->  '10':   a(3) = 2
.   4 ->  '11':   a(4) = 0
.   5 ->  '12':   a(5) = 0
.   6 ->  '20':   a(6) = 1
.   7 ->  '21':   a(7) = 0
.   8 ->  '22':   a(8) = 0
.   9 -> '100':   a(9) = 2
.  10 -> '101':  a(10) = 2
.  11 -> '102':  a(11) = 3  <-- 11 is the smallest 3-pandigital number
.  12 -> '110':  a(12) = 2
.  13 -> '111':  a(13) = 0
.  14 -> '112':  a(14) = 0
.  15 -> '120':  a(15) = 3.
		

Crossrefs

Cf. A007089, A067898 (decimal).

Programs

  • Haskell
    import Data.List (delete)
    a212193 n = f n [0..3] where
       f x ys | x <= 2    = head $ delete x ys
              | otherwise = f x' $ delete d ys where (x',d) = divMod x 3
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