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A063836
Numbers n such that usigma(sigma(n)) is prime.
0
3, 217, 57337
OFFSET
1,1
MATHEMATICA
us[n_Integer] := (d = Divisors[n]; l = Length[d]; k = 1; s = n; While[k < l, If[ GCD[ d[[k]], n/d[[k]] ] == 1, s = s + d[[k]]]; k++ ]; s); Do[m = n; If[ PrimeQ[ us[ DivisorSigma[1, n]]], Print[n]], {n, 1, 10^7/4} ]
CROSSREFS
Cf. A063103.
Sequence in context: A225239 A225362 A373055 * A172811 A247070 A140441
KEYWORD
nonn,bref
AUTHOR
Robert G. Wilson v, Aug 21 2001
STATUS
approved