OFFSET
1,2
LINKS
Michel Marcus, Table of n, a(n) for n = 1..500
EXAMPLE
1(k = 1); 2(1); 3(3); 4(2); 9(1); 12(2, 3, 12); 14(14); 20(4); 24(6); ...
MAPLE
filter:= n -> ormap(t -> numtheory:-sigma(n+t) mod n = 0, numtheory:-divisors(n)): # Robert Israel, Mar 14 2017
MATHEMATICA
Select[Range@ 1680, Function[n, Total@ Boole@ Map[Function[k, Divisible[DivisorSigma[1, n + k], n]], Divisors@ n] > 0]] (* Michael De Vlieger, Mar 15 2017 *)
ndsQ[n_]:=AnyTrue[DivisorSigma[1, n+Divisors[n]], Mod[#, n]==0&]; Select[ Range[ 2000], ndsQ] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Aug 11 2018 *)
PROG
(PARI) isok(n) = fordiv (n, d, if (! (sigma(n+d) % n), return (1))); \\ Michel Marcus, Mar 15 2017
CROSSREFS
KEYWORD
nonn
AUTHOR
Juri-Stepan Gerasimov, Mar 14 2017
STATUS
approved