A065871 Numbers k such that usigma(k) + 1 is a prime.

1, 3, 5, 6, 9, 10, 11, 17, 18, 20, 22, 24, 26, 27, 28, 29, 30, 38, 41, 42, 44, 45, 46, 50, 51, 52, 55, 56, 59, 62, 69, 71, 76, 77, 80, 81, 82, 85, 88, 90, 91, 98, 100, 101, 104, 105, 106, 107, 112, 114, 116, 118, 125, 126, 132, 136, 137, 140, 141, 145, 146, 148, 149

Offset

1,2

Links

Harry J. Smith, Table of n, a(n) for n = 1..1000

Mathematica

f[n_] := Block[ {a = FactorInteger[n], k = l = s = 1}, l = Length[a]; While[k <= l, s = s * (a[[k, 1]]^a[[k, 2]] + 1); k++ ]; Return[s]]; Select[ Range[200], PrimeQ[ f[ # ] + 1] & ]

Prog

(PARI) usigma(n)= { local(f, s=1); f=factor(n); for(i=1, matsize(f)[1], s*=1 + f[i, 1]^f[i, 2]); return(s) } { n=0; for (m=1, 10^9, if (isprime(usigma(m) + 1), write("b065871.txt", n++, " ", m); if (n==1000, return)) ) } \\ Harry J. Smith, Nov 02 2009

Crossrefs

Cf. A034448.

Sequence in context: A270198 A133512 A344154 * A128291 A304434 A334133

Adjacent sequences: A065868 A065869 A065870 * A065872 A065873 A065874

Keyword

nonn

Author

Robert G. Wilson v, Dec 07 2001

Status

approved