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 A074991 #21 Aug 07 2015 02:46:31
%S A074991 4,41,78,115,152,189,226,263,2970,30337,33704,37071,40438,43805,47172,
%T A074991 50539,53906,57273,60640,64007,67374,70741,74108,77475,80842,84209,
%U A074991 87576,90943,94310,97677,101044,104411,107778,111145,114512
%N A074991 Concatenation of n, n+1, n+2 divided by 3.
%C A074991 If all the three numbers have the same number of digits then the terms are in A.P. with a common difference that follows a pattern with increase in number of digits. E.g. for n = 1 to 7 the common difference, c.d. = 37. For n = 10 to 97 c.d. = 3367, For three digit numbers from 100 to 997 it is 333667 etc.
%e A074991 a(4) = 456/3 = 152.
%p A074991 read("transforms") ;
%p A074991 A074991 := proc(n)
%p A074991 digcatL([n,n+1,n+2]) ;
%p A074991 %/3 ;
%p A074991 end proc:
%p A074991 seq(A074991(n),n=0..50) ; # _R. J. Mathar_, Oct 04 2011
%t A074991 f[n_] := FromDigits@ Flatten@ IntegerDigits[{n, n + 1, n + 2}]/3; Array[f, 26, 0] (* _Robert G. Wilson v_ *)
%Y A074991 Cf. A074992.
%Y A074991 Equals (1/3) A001703.
%K A074991 base,nonn
%O A074991 0,1
%A A074991 _Amarnath Murthy_, Aug 31 2002
%E A074991 Incorrect conjecture deleted by _Colin Barker_, Sep 26 2013