A070275 -id:A070275 - cp's OEIS frontend

A057531 Numbers whose sum of digits and number of divisors are equal.

1, 2, 11, 22, 36, 84, 101, 152, 156, 170, 202, 208, 225, 228, 288, 301, 372, 396, 441, 444, 468, 516, 525, 530, 602, 684, 710, 732, 804, 828, 882, 952, 972, 1003, 1016, 1034, 1070, 1072, 1106, 1111, 1164, 1236, 1304, 1308, 1425, 1472, 1476, 1521, 1524

Offset: 1

Asher Auel, Sep 03 2000

[A007953(n)/A000005(n) = c] AND [A000005(n)/A007953(n) = c], c an integer. - Ctibor O. Zizka, Jun 26 2009

			36 is a term as the sum of the digits of 36 is 3+6 = 9 and the number of divisors is 9 too.

Giovanni Resta, Table of n, a(n) for n = 1..10000 (first 210 terms from Daniel Arribas)
Code Golf StackExchange, Find the nth number where the digit sum equals the number of factors, coding challenge started Nov 28 2022.

Cf. A000005, A007953, A057532, A050689, A070274, A070275, A063737, A067077.

Select[ Range[ 1000 ], DivisorSigma[ 0, # ]==Plus@@IntegerDigits[ # ]& ] (* Harvey P. Dale, Feb 19 2004 *)

A050689 Composites whose sum of digits equals number of its prime factors, with multiplicity.

Original entry on oeis.org

12, 30, 32, 40, 102, 220, 240, 500, 600, 1002, 1012, 1104, 1152, 1210, 1320, 1500, 2001, 2002, 2020, 2040, 2120, 2240, 2300, 3010, 3040, 3300, 4032, 4100, 4320, 5100, 5200, 6400, 7000, 7200, 10001, 10002, 10011, 10030, 10040, 10080, 10140, 10220, 10304, 10800

Offset: 1

Patrick De Geest, Aug 15 1999

The sequence is infinite because there are infinitely many primes whose sum of digits is odd (see related comment in A119450). Let p be one of them, and let k be its digital sum. Then p*10^((k-1)/2) is a term. For example, 41*10^2 is a term. - Metin Sariyar, May 30 2020

			2002 is a term since 2+0+0+2 = 4, and 2002 = 2*7*11*13 has 4 prime factors.

Giovanni Resta, Table of n, a(n) for n = 1..10000 (first 322 terms from Michael Turniansky)

Cf. A050690, A057531, A057532, A070274, A070275, A063737, A067077, A119450.

Select[Range[10300],!PrimeQ[#]&&PrimeOmega[#]==Total[IntegerDigits[#]]&] (* Jayanta Basu, May 30 2013 *)

isok(n) = sumdigits(n) == bigomega(n); \\ Michel Marcus, Feb 13 2017

from sympy import factorint
def ok(n): return 1 < sum(map(int, str(n))) == sum(factorint(n).values())
print([k for k in range(11000) if ok(k)]) # Michael S. Branicky, Dec 30 2021

A067077 Numbers whose product of distinct prime factors is equal to its sum of digits.

Original entry on oeis.org

1, 2, 3, 5, 6, 7, 24, 375, 392, 640, 2401, 4802, 4913, 6400, 7744, 17576, 42592, 64000, 106496, 234256, 295936, 468750, 546875, 628864, 640000, 877952, 1124864, 1966080, 2839714, 3687936, 4687500, 4816896, 4952198, 6400000, 6453888

Offset: 1

Joseph L. Pe, Feb 18 2002

The product of the distinct prime factors of n (the squarefree kernel of n) is also denoted by rad(n) = A007947(n). - Giovanni Resta, Apr 21 2017

			The prime factors of 375 are 3,5, which have product = 15, the sum of the digits of 375, so 375 is a term of the sequence.

Giovanni Resta, Table of n, a(n) for n = 1..10000 (first 71 terms from Harry J. Smith)

Cf. A007947, A006753, A057531, A057532, A050689, A070274, A070275, A063737, A285494.

f[n_] := Times@@ (First/@ FactorInteger[n]); g[n_] := Plus @@ IntegerDigits[n]; Select[Range[10^5], f[#] == g[#] &] (* or *)
nd=12; up=10^nd; L={1}; Do[If[SquareFreeQ[su], ps = First /@ FactorInteger[su]; nps = Length@ ps; Clear[ric]; ric[n_, i_] := Block[{e = 0, m}, If[i > nps, If[Plus @@ IntegerDigits[su n] == su, Sow[su n]], While[ (m = n ps[[i]]^e ) su < up, ric[m, i+1]; e++]]]; z = Reap[ ric[1, 1]][[2]]; If[z != {}, L = Union[L, z[[1]]]]], {su, 2, 9 nd}]; L (* fast, terms < 10^12, Giovanni Resta, Apr 21 2017 *)
Select[Range[65*10^5],Times@@FactorInteger[#][[All,1]]==Total[ IntegerDigits[ #]]&] (* Harvey P. Dale, Dec 16 2018 *)

isok(k)={vecprod(factor(k)[,1]) == sumdigits(k)} \\ Harry J. Smith, May 06 2010

a(19)-a(35) from Donovan Johnson, Sep 29 2009

a(1)=1 prepended by Giovanni Resta, Apr 21 2017

A070274 Numbers n such that sum of digits of n equals the squarefree part of n.

Original entry on oeis.org

1, 2, 3, 5, 6, 7, 12, 24, 100, 150, 200, 300, 320, 375, 500, 600, 640, 700, 704, 735, 832, 960, 1014, 1088, 1200, 1815, 2023, 2400, 2535, 2940, 3549, 3610, 3840, 4046, 4335, 4913, 5054, 5376, 5415, 5491, 6069, 6137, 6358, 6647, 7260, 7581, 7942, 8959, 9386

Offset: 1

Benoit Cloitre, May 09 2002

The squarefree part of x, core(x), is the smallest integer such that x*core(x) is a square.

Giovanni Resta, Table of n, a(n) for n = 1..10000

Cf. A007913, A057531, A057532, A050689, A070275, A063737, A067077, A285494.

core[n_]:=Block[{f=FactorInteger[n], p, e}, {p, e} = Transpose[f]; Times@@ (p^Mod[e, 2])]; Select[Range[10^4], core[#] == Plus @@ IntegerDigits[#] &] (* Giovanni Resta, Apr 21 2017 *)

list(lim)=my(v=List()); forfactored(n=1,lim\1, if(core(n)==sumdigits(n[1]), listput(v,n[1]))); Vec(v) \\ Charles R Greathouse IV, Nov 05 2017

Data corrected by Giovanni Resta, Apr 21 2017

A285494 Numbers k such that digit sum of k = number of distinct prime factors of k.

Original entry on oeis.org

20, 30, 102, 120, 200, 300, 1002, 1200, 2000, 2001, 2002, 3000, 3010, 10001, 10002, 10011, 10030, 10120, 11001, 11020, 11110, 12000, 20000, 20001, 21010, 30000, 30030, 30100, 100001, 100030, 100101, 100130, 100210, 100300, 101001, 101101, 101200, 102102, 110001, 110200

Offset: 1

Jonathan Frech, Apr 19 2017

Giovanni Resta, Table of n, a(n) for n = 1..10000

Cf. A001221, A007953, A057531, A057532, A050689, A070274, A070275, A063737, A067077.

Select[Range[2,10000],Total[IntegerDigits[#]]==Length[FactorInteger[#]]&] (* or *)
nd = 10; s = 1; Sort@ Flatten@ Reap[ While[ Times @@ Prime[ Range@ s] < 10^nd, pa = IntegerPartitions[s, {nd}, Range[0, 9]]; Do[Sow@ Select[ FromDigits /@ Permutations[p], PrimeNu[#] == s &], {p, pa}]; s++]][[2, 1]] (* terms < 10^10, Giovanni Resta, Apr 21 2017 *)

isok(n) = sumdigits(n) == omega(n); \\ Michel Marcus, Apr 20 2017

More terms from Michel Marcus, Apr 20 2017

A050690 Sum of digits of zero-absent composite a(n) equals number of prime factors.

Original entry on oeis.org

12, 32, 1152, 11232, 13122, 14112, 21312, 111132, 112112, 3121152, 11231232, 11354112, 812122112, 1251213312, 2211121152, 2211213312, 5121114112, 26122125312, 56321114112, 62214111232, 431711322112, 3421411213312, 11111212122112, 11112113242112

Offset: 1

Patrick De Geest, Aug 15 1999

10^11 < a(21) <= 431711322112. a(22) <= 3421411213312. - Donovan Johnson, May 30 2010

Do all terms end in 2, i.e., is each term = 2 mod 10? - Harvey P. Dale, May 26 2024

			E.g., 21312 (no zero in the string) gives 2+1+3+1+2 = 9 prime factors, namely, 2*2*2*2*2*2*3*3*37.

Cf. A050689, A057531, A057532, A070274, A070275, A063737, A067077.

t={}; Do[If[FreeQ[x=IntegerDigits[n],0]&&PrimeOmega[n]==Total[x],AppendTo[t,n]],{n,2,3220000,2}]; t (* Jayanta Basu, May 30 2013 *)

a(15)-a(20) from Donovan Johnson, May 30 2010
a(21)-a(22) confirmed by Giovanni Resta, Jun 02 2013
a(23)-a(24) from Giovanni Resta, Apr 23 2017

A356981 Numbers k such that the sum of distinct digits of k equals the sum of the prime divisors of k.

Original entry on oeis.org

2, 3, 5, 7, 84, 144, 160, 250, 343, 468, 735, 936, 975, 1125, 1215, 1375, 1408, 1600, 1694, 1872, 2401, 2500, 2646, 2880, 3920, 4913, 6084, 6318, 6860, 7296, 7695, 8624, 8704, 8788, 9126, 10125, 10240, 10816, 11264, 12672, 12675, 14641, 14896, 16000

Offset: 1

Tanya Khovanova, Sep 09 2022

Similar to A070275, where distinctness of digits is not required.

			144 = 2^4*3^2 and 1+4=2+3. Thus, 144 is in this sequence.

Cf. A070275, A217928.

Select[Range[2, 20000],Total[Union[IntegerDigits[#]]] ==  Total[Transpose[FactorInteger[#]][[1]]] &]

isok(k) = vecsum(Set(digits(k))) == vecsum(factor(k)[, 1]); \\ Michel Marcus, Sep 12 2022

from itertools import count, islice
from sympy import primefactors
def A356981_gen(startvalue=1): # generator of terms >= startvalue
    return filter(lambda k:sum(int(d) for d in set(str(k)))==sum(primefactors(k)), count(max(startvalue,1)))
A356981_list = list(islice(A356981_gen(),30)) # Chai Wah Wu, Sep 12 2022

A376157 Numbers k such that the sum of the digits of k equals the sum of its prime factors plus the sum of the multiplicities of each prime factor.

Original entry on oeis.org

4, 25, 36, 54, 125, 192, 289, 297, 343, 392, 448, 676, 756, 1089, 1536, 1764, 1936, 2646, 2888, 3872, 4802, 4860, 6174, 6250, 6776, 6860, 7290, 7488, 7680, 8750, 8775, 9408, 9747, 10648, 14739, 15309, 16848, 18432, 18865, 21296, 22869, 25725, 29988, 33750, 33957

Offset: 1

Jordan Brooks, Sep 12 2024

			For k = 54, its prime factorization is 2^1*3^3: 5+4 = 2+1+3+3 = 9.
For k = 756, its prime factorization is 2^2*3^3*7^1: 7+5+6 = 2+2+3+3+7+1 = 18.

Similar to A006753, A019506, A050689, A063737, A070275, A285494.

Cf. A007953, A008474.

Select[Range[34000], DigitSum[#]==Total[Flatten[FactorInteger[#]]] &] (* Stefano Spezia, Sep 14 2024 *)

isok(k)={my(f=factor(k)); vecsum(f[,1]) + vecsum(f[,2]) == sumdigits(k)} \\ Andrew Howroyd, Sep 26 2024

from sympy.ntheory import factorint
c = 2
while c < 10000:
    charsum = 0
    for char in str(c):
        charsum += int(char)
    pf = factorint(c)
    cand = 0
    for p in pf.keys():
        cand += p
        cand += pf[p]
    if charsum == cand:
        print(c)
        print(pf)
    c += 1

{ k : A007953(k) = A008474(k) }.

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A057531 Numbers whose sum of digits and number of divisors are equal.

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A050689 Composites whose sum of digits equals number of its prime factors, with multiplicity.

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A067077 Numbers whose product of distinct prime factors is equal to its sum of digits.

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A070274 Numbers n such that sum of digits of n equals the squarefree part of n.

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A285494 Numbers k such that digit sum of k = number of distinct prime factors of k.

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A050690 Sum of digits of zero-absent composite a(n) equals number of prime factors.

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A356981 Numbers k such that the sum of distinct digits of k equals the sum of the prime divisors of k.

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A376157 Numbers k such that the sum of the digits of k equals the sum of its prime factors plus the sum of the multiplicities of each prime factor.

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