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 A119564 #22 Jun 30 2024 20:58:42 %S A119564 2,3,13,249,65521,4294967265,18446744073709551553, %T A119564 340282366920938463463374607431768211329, %U A119564 115792089237316195423570985008687907853269984665640564039457584007913129639681 %N A119564 Define F(n) = 2^(2^n)+1 = n-th Fermat number, M(n) = 2^n-1 = the n-th Mersenne number. Then a(n) = F(n)-M(n)-1 = 2^(2^n) - 2^n + 1. %C A119564 The numbers n that divide a(n) are A373580. - _Thomas Ordowski_, Jun 11 2024 %F A119564 a(n) = (2^(2^n) - 1) - (2^n - 2). - _Thomas Ordowski_, Jun 11 2024 %e A119564 F(2) = 2^(2^2)+1 = 17, M(2) = 2^2-1 = 3, F(2)-M(2)-1 = 13. %o A119564 (PARI) fm4(n) = for(x=0,n,y=2^(2^x)+1-(2^x-1)-1;print1(y",")) %Y A119564 Cf. A119550, A119563, A307843, A373580. %K A119564 nonn %O A119564 0,1 %A A119564 _Cino Hilliard_, May 31 2006 %E A119564 Edited by _N. J. A. Sloane_, Jun 03 2006 %E A119564 Definition corrected by _R. J. Mathar_, May 15 2007