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 A286381 #6 Feb 16 2025 08:33:45 %S A286381 2,5,16,12,67,9,16,23,436,80,1771,18,67,80,1771,668,16111,48,277,302, %T A286381 7141,2630,64621,14,16,23,436,80,1771,31,436,467,21946,1832,87991,94, %U A286381 1771,1832,87991,16292,793171,328,7141,7262,352381,64982,3173941,25,67,80,1771,668,16111,94,1771,1832,87991,16292,793171,706,16111,16292,793171,405452,19841851 %N A286381 Compound filter: a(n) = P(A055881(n), A278236(n)), where P(n,k) is sequence A000027 used as a pairing function. %H A286381 Antti Karttunen, <a href="/A286381/b286381.txt">Table of n, a(n) for n = 1..10080</a> %H A286381 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/PairingFunction.html">Pairing Function</a> %H A286381 <a href="/index/Fa#facbase">Index entries for sequences related to factorial base representation</a> %F A286381 a(n) = (1/2)*(2 + ((A055881(n)+A278236(n))^2) - A055881(n) - 3*A278236(n)). %o A286381 (Scheme) (define (A286381 n) (* (/ 1 2) (+ (expt (+ (A055881 n) (A278236 n)) 2) (- (A055881 n)) (- (* 3 (A278236 n))) 2))) %Y A286381 Cf. A000027, A055881, A278236, A286382, A286143. %K A286381 nonn %O A286381 1,1 %A A286381 _Antti Karttunen_, May 08 2017