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 A103508 #8 Jul 23 2025 17:09:38 %S A103508 9,15,31,101,139,227,91,503,995,451,751,539,1819,1397,2957,3461,1831, %T A103508 1417,6023,3769,1777,9587,5411,9421,18653,8089,4511,6541,10529,16051, %U A103508 19049,13163,3139,22937,23929,43363,24919,43571,97367,55571,14419,75209 %N A103508 a(n) = 1 + 2 * least i such that A103507(i)=n+1, 0 if no such i exists. %o A103508 (Scheme) (define (A103508 n) (+ 1 (* 2 (first-n-where-fun_n-is-i1 A103507 (+ 1 n))))) %o A103508 (define (first-n-where-fun_n-is-i1 fun i) (let loop ((n 1)) (cond ((= i (fun n)) n) (else (loop (+ n 1)))))) %Y A103508 Cf. A103510, A103151, A103152, A103153, A103506, A103507, A025017. %K A103508 nonn,hard %O A103508 1,1 %A A103508 _Lei Zhou_, Feb 10 2005 %E A103508 Edited and Scheme-code added by _Antti Karttunen_, Jun 19 2007