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 A278512 #6 Nov 24 2016 09:29:08 %S A278512 1,2,4,3,6,5,7,8,10,12,9,17,11,23,15,30,13,38,16,47,14,57,18,68,21,80, %T A278512 22,93,24,107,28,122,19,138,31,155,20,173,29,192,39,212,36,233,25,255, %U A278512 48,278,37,302,27,327,58,353,26,380,32,408,69,437,45,467,46,498,81,530,55,563,40,597,94,632,35,668,33 %N A278512 Inverse permutation to A278511. %H A278512 Antti Karttunen, <a href="/A278512/b278512.txt">Table of n, a(n) for n = 1..10000</a> %H A278512 <a href="/index/Per#IntegerPermutation">Index entries for sequences that are permutations of the natural numbers</a> %F A278512 a(n) = (1/2) * ((c+r)^2 - r - 3*c + 2), where c = A278537(n) and r = A278538(n). %o A278512 (define (A278512 n) (if (= 1 n) n (let ((row (A278538 n)) (col (A278537 n))) (+ 1 (* (/ 1 2) (- (expt (+ row col) 2) row col col col -2)))))) %Y A278512 Inverse: A278511. %Y A278512 Cf. A278537, A278538. %Y A278512 Cf. also A278504, A278506. %K A278512 nonn %O A278512 1,2 %A A278512 _Antti Karttunen_, Nov 23 2016