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A057708 Numbers n such that 2^n reversed is prime. 7
1, 4, 5, 7, 10, 17, 24, 37, 45, 55, 70, 77, 107, 137, 150, 271, 364, 1157, 1656, 2004, 2126, 3033, 3489, 3645, 4336, 6597, 7279, 12690, 13840, 20108, 21693, 28888, 84155, 102930 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

a(35) > 105000. - Giovanni Resta, Feb 22 2013

LINKS

Table of n, a(n) for n=1..34.

EXAMPLE

4 is a member because 2^4 reversed is 61 and prime.

MAPLE

with(numtheory): myarray := []: for n from 1 to 4000 do it1 := convert(2^n, base, 10): it2 := sum(10^(nops(it1)-i)*it1[i], i=1..nops(it1)): if isprime(it2) then printf(`%d, `, n) fi: od:

MATHEMATICA

Do[ If[ PrimeQ[ FromDigits[ Reverse[ IntegerDigits[2^n]] ]], Print[ n]], {n, 20000}] (* Robert G. Wilson v, Jan 29 2005 *)

CROSSREFS

Sequence in context: A145018 A018910 A022936 * A032686 A074300 A047375

Adjacent sequences:  A057705 A057706 A057707 * A057709 A057710 A057711

KEYWORD

base,nonn,more

AUTHOR

G. L. Honaker, Jr., Oct 23 2000

EXTENSIONS

More terms from Chris Nash (chris_nash(AT)prodigy.net), Oct 25 2000

Two more terms from Robert G. Wilson v, Jan 29 2001

3 more terms from Farideh Firoozbakht, Aug 05 2004

a(33)-a(34) from Giovanni Resta, Feb 22 2013

STATUS

approved

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Last modified March 29 13:14 EDT 2017. Contains 284270 sequences.