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 A057777 #13 Mar 16 2025 13:11:02 %S A057777 1,2,4,40,16,96,192,640,256,7680,13312,18432,12288,40960,114688, %T A057777 163840,65536,1179648,786432,5767168,7340032,23068672,104857600, %U A057777 377487360,754974720,167772160,469762048,2013265920,3489660928,12348030976,3221225472,75161927680,184683593728 %N A057777 a(n) is the smallest number such that a(n)+1 is a prime and the largest power of 2 which divides it is 2^n. %H A057777 Amiram Eldar, <a href="/A057777/b057777.txt">Table of n, a(n) for n = 0..1000</a> %F A057777 a(n) = A057775(n) - 1. - _Sean A. Irvine_, Jun 27 2022 %e A057777 The 4th term is 40. It is divisible by 8, 40+1 = 41 is prime. Smaller multiples of 8 are not suitable because, e.g., albeit 8|16 and 16+1 = 17 is a prime, but the largest power of 2 that divides 16 is not 8, it is 16. So 16 is not the 3rd, it is the 4th term here. %Y A057777 Cf. A000040, A006093, A057775, A057776. %K A057777 nonn %O A057777 0,2 %A A057777 _Labos Elemer_, Nov 02 2000 %E A057777 More terms from Larry Reeves (larryr(AT)acm.org), Nov 03 2000