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 A057708 Numbers n such that 2^n reversed is prime. 10

%I

%S 1,4,5,7,10,17,24,37,45,55,70,77,107,137,150,271,364,1157,1656,2004,

%T 2126,3033,3489,3645,4336,6597,7279,12690,13840,20108,21693,28888,

%U 84155,102930

%N Numbers n such that 2^n reversed is prime.

%C a(35) > 105000. - _Giovanni Resta_, Feb 22 2013

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

%p 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:

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

%K base,nonn,more

%O 1,2

%A _G. L. Honaker, Jr._, Oct 23 2000

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

%E Two more terms from _Robert G. Wilson v_, Jan 29 2001

%E 3 more terms from _Farideh Firoozbakht_, Aug 05 2004

%E a(33)-a(34) from _Giovanni Resta_, Feb 22 2013

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Last modified January 26 05:40 EST 2020. Contains 331273 sequences. (Running on oeis4.)