OFFSET
1,1
LINKS
Harry J. Smith, Table of n, a(n) for n = 1..1000
EXAMPLE
p=71 appears in the sequence at 9th, 16th, 17th and 19th positions as -1+sigma(x) for x=30, 46, 51, 55.
MATHEMATICA
Do[s=-1+DivisorSigma[1, n]; If[PrimeQ[s]&&!PrimeQ[n], Print[s]], {n, 1, 256}]
PROG
(PARI) { n=0; for (m=1, 10^9, if (!isprime(m) && isprime(p=sigma(m) - 1), write("b066074.txt", n++, " ", p); if (n==1000, return)) ) } \\ Harry J. Smith, Nov 10 2009
(PARI) lista(nn) = forcomposite(n=1, nn, if (isprime(p=(sigma(n)-1)), print1(p, ", "))); \\ Michel Marcus, Jan 05 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
Labos Elemer, Dec 03 2001
STATUS
approved