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 A254047 #7 Feb 01 2015 10:02:34 %S A254047 1,2,3,6,4,10,15,5,21,28,9,36,45,7,55,66,14,78,91,20,105,120,8,136, %T A254047 153,27,171,190,35,210,231,13,253,276,44,300,325,54,351,378,11,406, %U A254047 435,65,465,496,77,528,561,19,595,630,90,666,703,104,741,780,26,820,861,119,903,946,135,990,1035,12,1081,1128,152,1176,1225,170,1275,1326,34 %N A254047 Inverse permutation to A191450. %H A254047 Antti Karttunen, <a href="/A254047/b254047.txt">Table of n, a(n) for n = 1..10000</a> %H A254047 <a href="/index/Per#IntegerPermutation">Index entries for sequences that are permutations of the natural numbers</a> %o A254047 (Scheme) %o A254047 (define (A254047 n) (let ((x (A253887 n)) (y (A254046 n))) (* (/ 1 2) (- (expt (+ x y) 2) x y y y -2)))) %Y A254047 Cf. A191450, A253887, A254046, A254052. %K A254047 nonn %O A254047 1,2 %A A254047 _Antti Karttunen_, Jan 24 2015