OFFSET
1,2
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
EXAMPLE
a(6) = 66 because sigma(6) = sigma(11) = 12; 6 * 11 = 66.
MAPLE
N:= 1000: # to get a(n) before the first n with sigma(n) > N
S:= map(numtheory:-sigma, [$1..N-1]):
m:=min(select(t -> S[t]>N, [$1..N-1]))-1:
seq(convert(select(s -> S[s]=S[n], [$1..S[n]-1]), `*`), n=1..m); # Robert Israel, Jul 04 2019
MATHEMATICA
a[n_] := Block[{s = DivisorSigma[1, n]}, Product[Which[s == DivisorSigma[1, k], k, True, 1], {k, s}]]; Array[a, 49] (* Giovanni Resta, Jul 03 2019 *)
PROG
(Magma) [&*[k: k in[1..10000] | SumOfDivisors(k) eq SumOfDivisors(n)]: n in [1..100]]
(PARI) a(n) = {my(s=sigma(n)); prod(k=1, s, if ((sigma(k)==s), k, 1)); } \\ Michel Marcus, May 12 2019
CROSSREFS
KEYWORD
nonn
AUTHOR
Jaroslav Krizek, May 12 2019
STATUS
approved