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 A255556 #8 Apr 19 2015 00:52:35 %S A255556 1,3,2,5,6,10,4,8,15,9,14,21,28,36,7,12,45,20,13,55,66,19,27,78,35,44, %T A255556 91,105,120,136,11,17,153,54,26,171,190,18,65,210,77,25,231,253,276, %U A255556 34,90,300,43,53,325,351,104,119,378,135,152,406,435,465,496,528,16,23,561,170,64,595,630,33,189,666,209,24 %N A255556 Inverse permutation to A255555. %H A255556 Antti Karttunen, <a href="/A255556/b255556.txt">Table of n, a(n) for n = 1..10000</a> %H A255556 <a href="/index/Per#IntegerPermutation">Index entries for sequences that are permutations of the natural numbers</a> %F A255556 a(n) = (1/2) * ((c+r)^2 - r - 3*c + 2), where c = A255559(n), and r = A255560(n). %o A255556 (Scheme) (define (A255556 n) (let ((col (A255559 n)) (row (A255560 n))) (* (/ 1 2) (- (expt (+ row col) 2) row col col col -2)))) %Y A255556 Inverse permutation: A255555. %Y A255556 Cf. A255558, A255559, A255560. %K A255556 nonn %O A255556 1,2 %A A255556 _Antti Karttunen_, Apr 14 2015