A256635 a(n) = the smallest number k such that the base-10 digital sum of sigma(k) is n.
1, 19, 2, 3, 13, 5, 4, 7, 10, 12, 28, 18, 192, 67, 42, 273, 52, 138, 324, 336, 196, 300, 372, 438, 2716, 997, 1590, 3468, 2512, 3260, 5817, 5692, 4112, 17472, 10852, 15840, 18496, 27252, 22860, 24300, 31572, 35172, 61488, 165652, 138438, 265252, 285652, 292860
Offset: 1
Examples
For n = 5; digital sum of sigma(13) = digital sum of 14 = 5. The number 13 is the smallest number with this property so a(5) = 13.
Links
- Max Alekseyev, Table of n, a(n) for n = 1..100 (terms for n = 1..66 from Chai Wah Wu)
Programs
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Magma
A256635:=func
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Maple
N := 10^6: # return all values before the first > N for n from 1 to N do v:= convert(convert(numtheory:-sigma(n),base,10),`+`); if not assigned(A[v]) then A[v]:= n fi; od: for count from 1 while assigned(A[count]) do od: seq(A[i],i=1..count-1); # Robert Israel, Apr 09 2015
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Mathematica
f[n_] := Block[{k = 1}, While[Plus @@ IntegerDigits[DivisorSigma[1, k]] != n, k++]; k]; Array[f, 48] (* Michael De Vlieger, Apr 07 2015 *) -
PARI
a(n) = {my(k = 1); while(sumdigits(sigma(k)) != n, k++); k;} \\ Michel Marcus, Apr 09 2015 -
Python
from sympy.ntheory.factor_ import divisor_sigma def A256635(n): k = 1 while sum(int(d) for d in str(divisor_sigma(k))) != n: k += 1 return k # Chai Wah Wu, Apr 18 2015
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