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 A286457 #6 Feb 16 2025 08:33:45 %S A286457 0,1,1,5,1,13,1,25,5,41,1,61,1,85,13,113,1,145,1,181,32,221,1,265,5, %T A286457 313,33,365,1,421,1,481,72,545,13,613,1,685,143,761,1,841,1,925,86, %U A286457 1013,1,1105,5,1201,219,1301,1,1405,32,1513,335,1625,1,1741,1,1861,201,1985,60,2113,1,2245,447,2381,1,2521,1,2665,223,2813,13,2965,1,3121,224,3281 %N A286457 Compound filter: a(n) = P(A078898(n), A246277(n)), with a(1) = 0, where P(n,k) is sequence A000027 used as a pairing function. %H A286457 Antti Karttunen, <a href="/A286457/b286457.txt">Table of n, a(n) for n = 1..10000</a> %H A286457 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/PairingFunction.html">Pairing Function</a> %F A286457 a(1) = 0 and for n > 1, a(n) = (1/2)*(2 + ((A078898(n)+A246277(n))^2) - A078898(n) - 3*A246277(n)). %o A286457 (Scheme) (define (A286457 n) (if (= 1 n) 0 (* (/ 1 2) (+ (expt (+ (A078898 n) (A246277 n)) 2) (- (A078898 n)) (- (* 3 (A246277 n))) 2)))) %Y A286457 Cf. A000027, A078898, A246277, A280492. %K A286457 nonn %O A286457 1,4 %A A286457 _Antti Karttunen_, May 14 2017