

A096820


Exponents k such that 2^k  21 is prime.


14



5, 6, 7, 9, 11, 13, 14, 21, 23, 41, 46, 89, 110, 389, 413, 489, 869, 1589, 1713, 2831, 10843, 11257, 16949, 24513, 39621, 43349, 62941, 96094, 139237, 145289, 264683, 396790
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OFFSET

1,1


COMMENTS

Similar to A057202 (which allows negative primes): this sequence is obtained by dropping the first four terms of A057202.  Joerg Arndt, Oct 05 2012


LINKS

Table of n, a(n) for n=1..32.
Henri Lifchitz and Renaud Lifchitz, Search for 2^n21, PRP Top Records


EXAMPLE

k=5: 32  21 = 11 is prime;
k=7: 128  21 = 107 is prime.


MATHEMATICA

Select[Range[5, 20000], PrimeQ[2^#21]&] (* Vladimir Joseph Stephan Orlovsky, Feb 27 2011 *)


PROG

(Sage)
def is_A096820(n):
t = 2^n21
return t > 1 and is_prime(t)
def A096820_list(up_to):
return [n for n in range(up_to) if is_A096820(n)]
A096820_list(100) # Peter Luschny, Oct 04 2012


CROSSREFS

Exponents for primes of 2^nd form: A000043 (d=1), A050414 (d=3), A059608 (d=5), A059609 (d=7), A059610 (d=9), A096817 (d=11), A096818 (d=13), A059612 (d=15), A059611 (d=17), A096819 (d=19), A096820 (d=21).
Cf. A096502
Sequence in context: A132829 A180061 A196029 * A175154 A355239 A030388
Adjacent sequences: A096817 A096818 A096819 * A096821 A096822 A096823


KEYWORD

nonn,more


AUTHOR

Labos Elemer, Jul 13 2004


EXTENSIONS

a(23)a(24) from Max Alekseyev, a(25) from Donovan Johnson, a(26)a(28) from Henri Lifchitz, a(29)a(30) from Lelio R Paula, added by Max Alekseyev, Feb 10 2012
a(31)a(32) from Lelio R Paula, added by Max Alekseyev, Oct 24 2013


STATUS

approved



