A065872 Numbers k such that usigma(k) - 1 is a prime (cf. A034448).

2, 3, 5, 6, 7, 10, 11, 12, 13, 14, 15, 17, 18, 19, 20, 21, 23, 26, 29, 30, 31, 33, 34, 35, 37, 38, 40, 41, 43, 44, 45, 46, 47, 48, 51, 53, 54, 55, 56, 57, 58, 59, 61, 63, 65, 67, 68, 71, 72, 73, 74, 75, 78, 79, 80, 83, 85, 86, 88, 89, 90, 93, 96, 97, 98, 101, 103, 105, 107

Offset

1,1

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("b065872.txt", n++, " ", m); if (n==1000, return)) ) } \\ Harry J. Smith, Nov 02 2009

Crossrefs

Cf. A034448.

Sequence in context: A317090 A361393 A179983 * A028741 A119316 A348964

Adjacent sequences: A065869 A065870 A065871 * A065873 A065874 A065875

Keyword

nonn

Author

Robert G. Wilson v, Dec 07 2001

Status

approved