%I
%S 2,5,3,549755813881,5,3,47,13,41,3,97,2011,23,536870869,17,11,5,3,61,
%T 953,439,433,173,167,31,67108763,409,149,19,911,140737488355201,16253,
%U 887,373,107,2147483497,32611,349,89,83,3917,331,16193,2096959,59,313,33554221
%N Smallest prime q such that q + prime(n) is a power of 2.
%C Corresponding exponents of 2: 2, 3, 3, 39, 4, 4, 6, 5, 6, 5, 7, 11, 6, 29, 6, 6, 6, 6, 7, 10, 9, 9, 8, 8, 7, 1, 9, 8, 7, 10, 47, 14, 10, 9, 8, 31, 15, 9, 8, 8, 12, 9, 14, 21, 8, 9, 1, ...
%H Robert Israel, <a href="/A191474/b191474.txt">Table of n, a(n) for n = 1..285</a>
%e 2+2 = 2^2, 3+5 = 2^3, 5+3 = 2^3, 7+549755813881 = 2^39, 11+5 = 2^4.
%p f:= proc(n) local p,m,t,q;
%p p:= ithprime(n);
%p for t from ilog2(p) do
%p q:= 2^t  p;
%p if isprime(q) then return q fi;
%p od;
%p end proc:
%p map(f, [$1..50]); # _Robert Israel_, Dec 23 2020
%K nonn
%O 1,1
%A _Zak Seidov_, Aug 28 2012
%E a(26) corrected by _Robert Israel_, Dec 23 2020
