

A128461


Numbers n such that 21^n  2 is a prime.


12



1, 2, 4, 10, 21, 25, 27, 32, 60, 88, 106, 120, 146, 264, 828, 965, 1944, 4822, 12089, 14427, 17354, 42335, 46395, 58348, 190632
(list;
graph;
refs;
listen;
history;
text;
internal format)



OFFSET

1,2


COMMENTS

a(26) > 2*10^5.  Robert Price, Jul 14 2015


LINKS

Table of n, a(n) for n=1..25.


MATHEMATICA

Do[ f = 21^n  2; If[ PrimeQ[ f ], Print[ {n, f} ] ], {n, 1, 1000} ]


CROSSREFS

Cf. A084714 = smallest prime of the form (2n1)^k  2, or 0 if no such number exists. Cf. A128472 = smallest prime of the form (2n1)^k  2 for k>(2n1), or 0 if no such number exists. Cf. A014224, A109080, A090669, A128455, A128457, A128458, A128459, A128460.
Sequence in context: A129211 A175204 A215533 * A011956 A018003 A328692
Adjacent sequences: A128458 A128459 A128460 * A128462 A128463 A128464


KEYWORD

hard,more,nonn


AUTHOR

Alexander Adamchuk, Mar 14 2007


EXTENSIONS

2 more terms from Stefan Steinerberger, May 05 2007
a(17)a(25) from Robert Price, Jul 14 2015


STATUS

approved



