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 A286461 #16 Feb 16 2025 08:33:45 %S A286461 1,5,4,9,22,5,4,32,4,5,121,9,46,437,4,20,121,17,4,24,4,5,67,14,22,17, %T A286461 4,24,121,5,4,2562,211,5,121,9,4,107,121,14,7261,5,211,24,4,17,121,41, %U A286461 4,2280,4,9,254,5,4,32,4,17,67,24,22,17,631,35,121,5,121,783,4,5,121,32,211,2280,4,9,67,17,4,41,121,5,254,9,46,2280,4,140,121,5,4,24 %N A286461 Compound filter (2-adic valuation of n & 4k+1,4k+3 prime-signature combination of 2n-1): a(n) = P(A001511(n), A286364((2*n)-1)), where P(n,k) is sequence A000027 used as a pairing function. %H A286461 Antti Karttunen, <a href="/A286461/b286461.txt">Table of n, a(n) for n = 1..10000</a> %H A286461 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/PairingFunction.html">Pairing Function</a> %H A286461 Indranil Ghosh, <a href="/A286461/a286461.txt">Python program to generate the sequence</a> %F A286461 a(n) = (1/2)*(2 + ((A001511(n)+A286364((2*n)-1))^2) - A001511(n) - 3*A286364((2*n)-1)). %o A286461 (Scheme) (define (A286461 n) (* (/ 1 2) (+ (expt (+ (A001511 n) (A286364 (+ n n -1))) 2) (- (A001511 n)) (- (* 3 (A286364 (+ n n -1)))) 2))) %Y A286461 Cf. A000027, A001511, A046523, A278223, A286161, A286364, A286371, A286372, A286463, A286465. %K A286461 nonn %O A286461 1,2 %A A286461 _Antti Karttunen_, May 10 2017