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 A139298 #14 Jul 10 2025 16:01:42 %S A139298 8,2048,576460752303423488, %T A139298 3618502788666131106986593281521497120414687020801267626233049500247285301248 %N A139298 a(n) = 2^(2p - 1)/4, where p is the n-th Mersenne prime A000668(n). %F A139298 a(n) = 2^(2*A000668(n) - 1)/4 = A139294(n)/4. %t A139298 a[n_] := 2^(2^(MersennePrimeExponent[n] + 1) - 5); Array[a, 4] (* _Amiram Eldar_, Jul 10 2025 *) %Y A139298 Cf. A000668, A139294, A139295, A139296, A139297, A139299, A139300, A139301, A139302, A139303, A139304, A139305, A139306. %K A139298 nonn %O A139298 1,1 %A A139298 _Omar E. Pol_, Apr 13 2008