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 A250252 #12 Nov 15 2014 16:49:56 %S A250252 1,2,3,4,6,7,10,5,15,11,21,16,28,9,36,22,45,29,55,14,66,37,78,8,91,20, %T A250252 105,46,120,56,136,27,153,13,171,67,190,35,210,79,231,92,253,44,276, %U A250252 106,300,12,325,54,351,121,378,19,406,65,435,137,465,154,496,77,528,26,561,172,595,90,630,191,666,211,703,104,741,18 %N A250252 Inverse permutation to A114881. %H A250252 Antti Karttunen, <a href="/A250252/b250252.txt">Table of n, a(n) for n = 1..8192</a> %H A250252 <a href="/index/Per#IntegerPermutation">Index entries for sequences that are permutations of the natural numbers</a> %F A250252 a(n) = 1 + ((((x+y)^2) - x - 3*y)/2), where x = A078898(n+1) and y = A055396(n+1). %F A250252 As a composition of related permutations: %F A250252 a(n) = A209268(A249812(n)). %F A250252 Other identities. For all n >= 1 the following holds: %F A250252 a(A005408(n-1)) = A000217(n). [Maps odd numbers to triangular numbers.] %F A250252 a(A006093(n)) = A000124(n-1). [Maps precedents of primes to central polygonal numbers.] %o A250252 (Scheme) (define (A250252 n) (let ((x (A078898 (+ 1 n))) (y (A055396 (+ 1 n)))) (* (/ 1 2) (- (expt (+ x y) 2) x y y y -2)))) %Y A250252 Inverse: A114881. %Y A250252 Similar or related permutations: A209268, A249812. %Y A250252 Cf. A000124, A000217, A005408, A006093, A055396, A078898. %Y A250252 Differs from A246274 for the first time at n=20, where a(20) = 14, while %Y A250252 A246274(20) = 20. %K A250252 nonn %O A250252 1,2 %A A250252 _Antti Karttunen_, Nov 15 2014