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 A256996 #9 Apr 19 2015 00:54:02 %S A256996 1,2,3,5,4,7,8,6,11,10,12,16,22,29,9,15,37,14,17,46,56,21,28,67,36,13, %T A256996 79,92,106,121,20,45,137,19,23,154,172,55,66,191,27,35,211,232,254,78, %U A256996 44,277,18,91,301,326,105,120,352,136,26,379,407,436,466,497,54,153,529,25,30,562,596,171,190,631,65,77,667,704,742,210,34,781,43 %N A256996 Inverse to A256995 considered as a permutation of natural numbers, with assumed fixed initial term a(1) = 1. %H A256996 Antti Karttunen, <a href="/A256996/b256996.txt">Table of n, a(n) for n = 1..10000</a> %H A256996 <a href="/index/Per#IntegerPermutation">Index entries for sequences that are permutations of the natural numbers</a> %F A256996 a(1) = 1, and for n > 1: a(n) = (1/2) * ((c+r)^2 - r - 3*c + 4), where c = A256989(n), and r = A256990(n). %o A256996 (Scheme) (define (A256996 n) (if (= 1 n) n (let ((col (A256989 n)) (row (A256990 n))) (+ 1 (* (/ 1 2) (- (expt (+ row col) 2) row col col col -2)))))) %Y A256996 Inverse: A256995. %Y A256996 Cf. A256989, A256990. %Y A256996 Cf. also A256998, A255556. %K A256996 nonn %O A256996 1,2 %A A256996 _Antti Karttunen_, Apr 14 2015