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 A061512 #13 Jun 24 2016 12:49:59
%S A061512 1,3,5,7,9,11,33,55,77,99,1111,3333,5555,7777,9999,11111111,33333333,
%T A061512 55555555,77777777,99999999,1111111111111111,3333333333333333,
%U A061512 5555555555555555,7777777777777777,9999999999999999,11111111111111111111111111111111,33333333333333333333333333333333
%N A061512 a(0) = 1; a(n) is obtained by incrementing each digit of a(n-1) by 2.
%C A061512 In A061511-A061522, A061746-A061750 when the incremented digit exceeds 9 it is written as a 2-digit string. So 9+1 becomes the 2-digit string 10, etc.
%C A061512 Also: odd repdigits (A010785) of length 2^k, cf. formula. - _M. F. Hasler_, Jun 24 2016
%F A061512 a(n) = (10^2^floor(n/5)-1)/9*(n%5*2+1), where n%5 means the remainder (in {0..4}) of n divided by 5. - _M. F. Hasler_, Jun 24 2016
%e A061512 Following 33: 3+2 = 5 and 3+2 = 5, hence the next term is 55.
%t A061512 NestList[FromDigits[Flatten[IntegerDigits/@(IntegerDigits[#]+2)]]&,1,30] (* _Harvey P. Dale_, Apr 13 2012 *)
%o A061512 (PARI) A061512(n)=10^2^(n\5)\9*(n%5*2+1) \\ _M. F. Hasler_, Jun 24 2016
%o A061512 (PARI) nxt(n) = my(d=digits(n)); if(d[1]<9,n+2*(10^#d - 1)/9,(10^(2*#d) - 1)/9)
%o A061512 inv(n) = {my(d=digits(n));5*logint(#d,2) + (d[1]+1)\2} \\ _David A. Corneth_, Jun 24 2016
%Y A061512 Cf. A061511 - A061522, A061746 - A061750; A061581 - A061587.
%Y A061512 Cf. also A010785.
%K A061512 base,nonn
%O A061512 0,2
%A A061512 _Amarnath Murthy_, May 08 2001
%E A061512 More terms from Larry Reeves (larryr(AT)acm.org), May 11 2001