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 A133139 #11 Jul 25 2020 07:23:35 %S A133139 0,0,1,2,3,5,6,10,9,12,14,17,20,20,20,29,28,31,35,35,37,40,45,51,49, %T A133139 55,55,58,64,61,71,76,74,76,78,87,92,91,99,97,107,100,114,107,112,119, %U A133139 128,132,133,127,142,140,151,146,151,154,170,158,172,164,185,179,184,186 %N A133139 Number of generalized Ulam sequences including n as the third or higher term. %C A133139 I generalize the Ulam sequence by allowing any positive integer values (i and j) for the first two terms. Subsequent terms are all those integers which are a unique sum of two distinct earlier terms. In this sequence, a(n) is the number of distinct sequences (as defined by the first two terms) where 1 <= i < n-1 and i < j <= n-1. %H A133139 Rémy Sigrist, <a href="/A133139/b133139.txt">Table of n, a(n) for n = 1..10000</a> %H A133139 Rémy Sigrist, <a href="/A133139/a133139.txt">C program for A133139</a> %e A133139 a(10) = 12, since 10 occurs as a term in 12 different generalized Ulam sequences. The first two values of each are: (1,3) (1,4) (1,5) (1,6) (1,7) (1,8) (1,9) (2,6) (2,8) (3,4) (3,7) (4,6). It does not occur in the sequence (1,2) which runs: 1, 2, 3, 4, 6, 8, 11... %o A133139 (C) See Links section. %Y A133139 Cf. A002858. %K A133139 nonn %O A133139 1,4 %A A133139 _Paul Richards_, Sep 21 2007 %E A133139 Spelling/notation corrections by _Charles R Greathouse IV_, Mar 18 2010