cp's OEIS Frontend

A294682 Numbers n such that A294386(n) = 2^(k-1)*(2^k - 2*n - 1) for some k such that 2^k - 2*n - 1 is prime.

%I A294682 #9 Feb 20 2018 22:51:14
%S A294682 0,12,62,121,126,205,241,877,1021,1022,1645,2041,2424,2761,2791,2965,
%T A294682 3355,3445,3541,4021,4081,4094,4165,4825,5071,5191,5251,5593,6151,
%U A294682 6385,6631,7465,7765,7884,8137,8188
%N A294682 Numbers n such that A294386(n) = 2^(k-1)*(2^k - 2*n - 1) for some k such that 2^k - 2*n - 1 is prime.
%e A294682 a(3) = 62 is in the sequence because A294386(62) = 192 = 2^6*3 where 2^7 - 2*62 - 1 = 3 is prime.
%p A294682 # Assuming A294386[n] has been assigned for n from 0 to N
%p A294682 Res:= NULL:
%p A294682 for n from 0 to N do
%p A294682   for k from ilog2(2*n+1)+1 do
%p A294682     p:= 2^k - 2*n-1;
%p A294682     if 2^(k-1)*p > A294386[n] then break fi;
%p A294682     if isprime(p) then
%p A294682       if A294386[n] = 2^(k-1)*p then Res:= Res, n fi;
%p A294682       break
%p A294682     fi
%p A294682   od
%p A294682 od:
%p A294682 Res;
%Y A294682 Cf. A096502, A294386.
%K A294682 nonn,more
%O A294682 1,2
%A A294682 _Robert Israel_, Nov 06 2017