OFFSET
1,1
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
EXAMPLE
102 is a member since the divisors of 102 are {1, 2, 3, 6, 17, 34, 51, 102} and 2 + 3 + ... + 51 = 113, a prime.
MAPLE
with(numtheory); b := []; for n from 3 to 2000 do t1 := divisors(n); t2 := convert(t1, list); t3 := add(t2[i], i=1..nops(t2)); if isprime(t3-1-n) then b := [op(b), n]; fi; od: b;
MATHEMATICA
f[n_]:=Plus@@Divisors[n]-n-1; lst={}; Do[a=f[n]; If[PrimeQ[a], AppendTo[lst, n]], {n, 7!}]; lst (* Vladimir Joseph Stephan Orlovsky, Sep 21 2009 *)
Select[Range[500], PrimeQ[DivisorSigma[1, #] - # - 1] &] (* Amiram Eldar, Dec 04 2020 *)
PROG
(PARI) isok(k) = isprime(sigma(k)-1-k); \\ Michel Marcus, Dec 04 2020
CROSSREFS
KEYWORD
nonn
AUTHOR
Chuck Seggelin (barkeep(AT)plastereddragon.com), Jul 05 2003
STATUS
approved