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 A248574 #17 Nov 15 2014 06:56:26 %S A248574 1,2,4,7,15,27,58,106,227,419,894,1662,3534,6606,14004,26292,55587, %T A248574 104739,220918,417526,878810,1665242,3498444,6644172,13934990, %U A248574 26517902,55531948,105863596,221384892,422711484,882865128,1688171496,3521765667,6742991139 %N A248574 a(n) = A027306(n) + A027306(n-1) for n > 0; a(0) = 1. %C A248574 Central terms of triangle in A249111. %H A248574 Reinhard Zumkeller, <a href="/A248574/b248574.txt">Table of n, a(n) for n = 0..1000</a> %o A248574 (Haskell) %o A248574 a248574 0 = 1 %o A248574 a248574 n = a027306 (n - 1) + a027306 n %Y A248574 Cf. A027306, A249111. %K A248574 nonn %O A248574 0,2 %A A248574 _Reinhard Zumkeller_, Nov 14 2014