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A242016
Smallest prime factor of A135972(n), the n-th composite Mersenne number.
2
3, 3, 3, 7, 3, 23, 3, 3, 7, 3, 3, 3, 7, 3, 47, 3, 31, 3, 7, 3, 233, 3, 3, 7, 3, 31, 3, 223, 3, 7, 3, 13367, 3, 431, 3, 7, 3, 2351, 3, 127, 3, 7, 3, 6361, 3, 23, 3, 7, 3, 179951, 3, 3, 7, 3, 31, 3, 193707721, 3, 7, 3
OFFSET
1,1
FORMULA
a(n) = A020639(A135972(n)).
PROG
(PARI) for(n=2, 1e2, if(!ispseudoprime(2^n-1), p=factor(2^n-1)[1, 1]; print1(p, ", ")))
CROSSREFS
Cf. A135972, A242017. Subsequence of A056608.
Sequence in context: A291767 A135087 A294505 * A084038 A346540 A326930
KEYWORD
nonn
AUTHOR
Felix Fröhlich, Aug 11 2014
STATUS
approved