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Least odd k such that (k*2^n)^2+k*2^n-1 is the first of twin primes with n>0.
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%I #4 Mar 31 2012 13:22:04

%S 1,5,1,11,9,89,25,359,187,11,145,309,559,47,115,41,87,1169,271,41,565,

%T 1005,1231,245,783,185,61,431,153,1205,423,465,2547,1257,891,351,25,

%U 945,937,431,453,4221,2763,251,783,1761,1381,2493,2125,5241,2871,255,4507

%N Least odd k such that (k*2^n)^2+k*2^n-1 is the first of twin primes with n>0.

%e (1*2^1)^2+1*2^1-1=5, 5 and 7 twin primes so k(1)=1

%e (1*2^2)^2+1*2^2-1=19 prime but 21 not prime

%e (3*2^2)^2+3*2^2-1=155 not prime

%e (5*2^2)^2+5*2^2-1=419, 419 and 421 twin primes so k(2)=5

%K nonn

%O 1,2

%A _Pierre CAMI_, Apr 09 2006