

A098472


Least k such that Mersenneprime(n)*2^k1 is prime (A000668(n)*2^k1), or 0 if no such k exists.


1



1, 1, 1, 25, 1, 5, 1, 97, 77, 19, 37
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OFFSET

1,4


COMMENTS

Conjecture: Mersenneprime(12) is a Riesel prime (that is, all numbers k^2*M(12)1 are composite for all k) and similarly for M(14) and M(15).
The sequence continues (>10000), 167, (>5000), (>5000), 1081, 371, 995, 909, 857, 33, (>150), (>150), ...


LINKS

Table of n, a(n) for n=1..11.


MATHEMATICA

mexp = {the list in A000043}; f[n_] := Block[{k = 1, mp = 2^mexp[[n]]  1}, While[ !PrimeQ[ mp*2^k  1] && k < 5000, k++ ]; If[k == 5000, 0, k]]; Do[ Print[ f[n]], {n, 20}] (* Robert G. Wilson v, Sep 11 2004 *)


CROSSREFS

Cf. A000043, A098471.
Sequence in context: A040641 A240981 A040640 * A040642 A040643 A040644
Adjacent sequences: A098469 A098470 A098471 * A098473 A098474 A098475


KEYWORD

hard,nonn


AUTHOR

Pierre CAMI, Sep 09 2004


EXTENSIONS

Edited by N. J. A. Sloane and Robert G. Wilson v, Sep 11 2004
a(19)a(21) from Robert G. Wilson v, Sep 11 2004


STATUS

approved



