

A101050


Least k such that prime(n)*2^k1 is prime, or 1 if no such k exists.


2



1, 0, 2, 1, 2, 3, 2, 1, 4, 4, 1, 1, 2, 7, 4, 2, 12, 3, 5, 2, 7, 1, 2, 4, 1, 10, 3, 10, 9, 8, 25, 2, 2, 1, 4, 5, 1, 3, 4, 2, 8, 3, 226, 3, 2, 1, 1, 3, 2, 1, 4, 4, 11, 6, 4, 2, 8, 1, 5, 2, 11, 2, 1, 26, 3, 6, 1, 1, 18, 3, 4, 4, 1, 7, 1, 2, 20, 5, 10, 3, 4, 7, 2, 3, 1, 6, 112, 9, 10, 7, 2, 12, 5, 46, 1, 2, 8
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OFFSET

1,3


COMMENTS

Primes p such that p*2^k1 is composite for all k are called Riesel numbers. The smallest known Riesel number is the prime 509203. Currently, 2293 is the smallest prime whose status is unknown. For a(120), which corresponds to the prime 659, Dave Linton found the least k is 800516.  T. D. Noe, Aug 04 2005


REFERENCES

See A046069


LINKS

Table of n, a(n) for n=1..97.


MATHEMATICA

Table[p=Prime[n]; k=0; While[ !PrimeQ[ 1+p*2^k], k++ ]; k, {n, 119}] (* T. D. Noe, Aug 04 2005 )


CROSSREFS

Cf. A046069 (least k such that (2n1)*2^k1 is prime).
Sequence in context: A134388 A055095 A048685 * A128979 A190167 A171565
Adjacent sequences: A101047 A101048 A101049 * A101051 A101052 A101053


KEYWORD

nonn


AUTHOR

Pierre CAMI, Jan 21 2005


EXTENSIONS

Corrected and extended by T. D. Noe, Aug 04 2005


STATUS

approved



