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A066074
Primes arising in A066073.
11
11, 17, 23, 23, 41, 31, 59, 41, 71, 47, 53, 47, 59, 89, 83, 71, 71, 97, 71, 79, 89, 167, 103, 83, 113, 139, 167, 223, 107, 131, 179, 233, 167, 127, 251, 191, 151, 239, 181, 179, 359, 167, 223, 311, 251, 239, 269, 191, 167, 179, 227, 233, 191, 239, 191, 293
OFFSET
1,1
LINKS
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
KEYWORD
nonn
AUTHOR
Labos Elemer, Dec 03 2001
STATUS
approved