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 A060511 #5 Jun 05 2013 14:39:15 %S A060511 0,0,1,2,3,4,0,1,2,3,4,5,6,7,8,0,1,2,3,4,5,6,7,8,9,10,11,12,0,1,2,3,4, %T A060511 5,6,7,8,9,10,11,12,13,14,15,16,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15, %U A060511 16,17,18,19,20,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20 %N A060511 Hexagonal excess: smallest amount by which n exceeds a hexagonal number (2k^2-k, A000384). %e A060511 a(19)=4 since 15(=2*3^2-3) is the largest hexagonal less than or equal to 19 and 19-15=4. %t A060511 Flatten[Range[#]&/@Differences[Array[#(2#-1)&,10,0]]-1] (* _Harvey P. Dale_, Jun 05 2013 *) %Y A060511 Cf. A002262, A053186, A055400, A060510. %K A060511 easy,nonn %O A060511 0,4 %A A060511 _Henry Bottomley_, Mar 22 2001