This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A156895 #16 Aug 01 2019 14:43:13
%S A156895 3,7,31,271,4591,151471,9845551,326409519151,
%T A156895 16455349947998422816223361143099916435126171767057238357700938736968751
%N A156895 Primes of the form 1 + Product_{j=0..k} (2^j + 1).
%C A156895 10th term has 150 digits. - _Emeric Deutsch_, Mar 07 2009
%C A156895 Primes of the form 1 + A028361(k), any k > 0. - _R. J. Mathar_, Jul 10 2011
%e A156895 (2^0 + 1)*(2^1 + 1)*(2^2 + 1)*(2^3 + 1)*(2^4 + 1) + 1 = 2*3*5*9*17 + 1 = 4591.
%p A156895 a := proc (n) if isprime(1+product(2^k+1, k = 0 .. n)) = true then 1+product(2^k+1, k = 0 .. n) else end if end proc: seq(a(n), n = 0 .. 40); # _Emeric Deutsch_, Mar 07 2009
%t A156895 Select[Table[Product[2^j+1,{j,0,k}],{k,0,30}]+1,PrimeQ] (* _Harvey P. Dale_, Aug 01 2019 *)
%Y A156895 Cf. A028361.
%K A156895 nonn
%O A156895 1,1
%A A156895 _J. M. Bergot_, Feb 17 2009
%E A156895 a(9) from _Emeric Deutsch_, Mar 07 2009