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A063836 Numbers n such that usigma(sigma(n)) is prime. 0
3, 217, 57337 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..3.

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: A300037 A225239 A225362 * A172811 A247070 A140441

Adjacent sequences:  A063833 A063834 A063835 * A063837 A063838 A063839

KEYWORD

nonn,bref

AUTHOR

Robert G. Wilson v, Aug 21 2001

STATUS

approved

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Last modified February 19 10:03 EST 2020. Contains 332041 sequences. (Running on oeis4.)