OFFSET
1,3
LINKS
Eric Weisstein's World of Mathematics, Refactorable Number
FORMULA
a(p) = p for odd primes p. - Wesley Ivan Hurt, Nov 28 2021
MATHEMATICA
a[n_] := DivisorSum[n, # &, !Divisible[#, DivisorSigma[0, #]] &]; Array[a, 100] (* Amiram Eldar, Nov 24 2021 *)
PROG
(PARI) a(n) = sumdiv(n, d, if (d%numdiv(d), d)); \\ Michel Marcus, Nov 24 2021
CROSSREFS
KEYWORD
nonn
AUTHOR
Wesley Ivan Hurt, Nov 23 2021
STATUS
approved