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 A143678 #4 Mar 31 2012 08:27:44
%S A143678 2,5,6,2,5,11,8,9,15,1,19,9,14,2,5,13,7,30,24,13,10,7,38,14,14,34,39,
%T A143678 11,6,26,1,7,6,17,38,5,12,23,32,3,54,30,11,6,59,17,18,69,2,69,39,2,23,
%U A143678 12,81,6,44,3,19,38,30,76,6,4,18,76,12,99,3,12,5,97,89,12,5,56,3,104,3,39,104,11,23,28,70,8,5,11,99,31,4,8
%N A143678 ( 1, 2, 3, 2^2, 5, 2*3, 7, 2^3, 3^2, 2*5, 11, 2^2*3, 13, 2*7, 3*5,..) becomes (abs (1-2+3, 2-2+5, 2-3+7, 2-3+3, 2-2+5, 11-2+2, 3-13+2, 7-3+5,..)).
%e A143678 Abs(1-2+3)=abs(2)=2=a(1).
%e A143678 Abs(2-2+5)=abs(5)=5=a(2).
%e A143678 Abs(2-3+7)=abs(6)=6=a(3).
%e A143678 Abs(2-3+3)=abs(2)=2=a(4).
%e A143678 Abs(2-2+5)=abs(5)=5=a(5).
%e A143678 Abs(11-2+2)=abs(11)=11=a(6).
%e A143678 Abs(3-13+2)=abs(-8)=8=a(7).
%e A143678 Abs(7-3+5)=abs(9)=9=a(8), etc.
%p A143678 pflat2 := proc(nmax) local a, ifs, n, p, c ; a := [1] ; for n from 2 to nmax do ifs := ifactors(n)[2] ; for p in ifs do a := [op(a),op(1,p)] ; if op(2,p) > 1 then a := [op(a),op(2,p)] ; fi; od: od: a ; end:
%p A143678 pL := pflat2(300) : for n from 1 to nops(pL)-4 by 3 do printf("%d,", abs(op(n, pL)-op(n+1, pL)+op(n+2,pL)) ) ; od: # _R. J. Mathar_, Nov 06 2008
%Y A143678 Cf. A141257, A141261.
%K A143678 nonn
%O A143678 1,1
%A A143678 _Juri-Stepan Gerasimov_, Nov 01 2008
%E A143678 Removed incompatibilities with internal OEIS format, extended _R. J. Mathar_, Nov 06 2008