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 A144020 #4 Mar 30 2012 17:39:40 %S A144020 4,7,10,12,13,15,18,19,20,22,23,25,27,28,30,31,34,35,36,37,39,42,43, %T A144020 44,45,46,47,49,50,51,52,54,55,57,58,60,62,63,66,67,68,69,70,71,73,74, %U A144020 75,76,77,78,79,82,83,84,85,87,89,90,91,92,94,95,97,98,99,100,102,103,105,106 %N A144020 Numbers of the form 1+i^2+j^2+k^2 with 1 <= i <= j <= k. %C A144020 No number == -1 mod 8 is a sum of three squares, so multiples of 8 are missing from this sequence. %C A144020 It appears that numbers == 1 mod 16 are also missing from the sequence. %F A144020 a(n) = 1+A000408(n). [From _R. J. Mathar_, Dec 03 2008] %K A144020 nonn %O A144020 1,1 %A A144020 _N. J. A. Sloane_, Dec 02 2008, Dec 21 2008