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 A139290 #18 May 07 2025 17:14:51 %S A139290 2,8,128,2048,524288,8388608,2147483648,34359738368,8796093022208, %T A139290 36028797018963968,576460752303423488,2361183241434822606848, %U A139290 604462909807314587353088,9671406556917033397649408 %N A139290 2^(2p - 1)/4, where p is prime. %F A139290 a(n) = A139286(n)/4. %t A139290 2^(2#-1)/4 & /@ Prime@ Range@ 15 (* _Harvey P. Dale_, Dec 16 2010 *) %o A139290 (Magma) [2^(2*p-1)div 4: p in PrimesUpTo(200)]; // _Vincenzo Librandi_, Dec 15 2010 %Y A139290 Cf. A139286, A139287, A139288, A139289, A139290, A139292, A139293, A139294, A139306. %K A139290 nonn %O A139290 1,1 %A A139290 _Omar E. Pol_, Apr 13 2008 %E A139290 More terms from _Jon E. Schoenfield_, Jul 16 2010