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 A259604 #4 Jun 30 2015 17:14:24 %S A259604 3,6,10,15,10,6,10,15,21,28,36,45,36,28,36,45,55,36,21,28,36,45,36,28, %T A259604 36,45,55,66,78,91,78,66,78,91,105,78,55,66,78,91,78,66,78,91,105,120, %U A259604 136,153,120,78,91,105,91,78,66,78,105,120,136,153,171,153 %N A259604 (A259542(n) + A259542(n+1)) / 2. %C A259604 All terms are triangular numbers by definition of A259542. %H A259604 Reinhard Zumkeller, <a href="/A259604/b259604.txt">Table of n, a(n) for n = 1..10000</a> %o A259604 (Haskell) %o A259604 a259604 n = a259604_list !! (n-1) %o A259604 a259604_list = zipWith ((flip div 2 .) . (+)) %o A259604 a259542_list $ tail a259542_list %Y A259604 Cf. A259542, A000217, A086517, A259602, A259603, A259605. %K A259604 nonn %O A259604 1,1 %A A259604 _Reinhard Zumkeller_, Jun 30 2015