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A256635 a(n) = the smallest number k such that the base-10 digital sum of sigma(k) is n. 2
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

a(n) = the smallest number k such that A007953(A000203(k)) = n.

Note that A007953(A000203(k)) is also A067342(k).

LINKS

Chai Wah Wu, Table of n, a(n) for n = 1..66

EXAMPLE

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.

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

MATHEMATICA

f[n_] := Block[{k = 1}, While[Plus @@ IntegerDigits[DivisorSigma[1, k]] != n, k++]; k]; Array[f, 48] (* Michael De Vlieger, Apr 07 2015 *)

PROG

(MAGMA) A256635:=func<n|exists(r){k:k in[1..10000000] | &+Intseq(SumOfDivisors(k)) eq n }select r else 0>; [A256635(n):n in[1..50]]

(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

CROSSREFS

Cf. A000203, A007953, A067342, A256642.

Sequence in context: A040357 A040358 A051312 * A040359 A040360 A040351

Adjacent sequences:  A256632 A256633 A256634 * A256636 A256637 A256638

KEYWORD

nonn,base

AUTHOR

Jaroslav Krizek, Apr 06 2015

STATUS

approved

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Last modified November 13 07:13 EST 2019. Contains 329085 sequences. (Running on oeis4.)