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 A256577 #21 Nov 16 2022 09:45:28
%S A256577 0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,40,41,42,43,44,45,
%T A256577 46,47,48,49,90,91,92,93,94,95,96,97,98,99,160,161,162,163,164,165,
%U A256577 166,167,168,169,250,251,252,253,254,255,256,257,258,259,360,361,362,363,364,365,366,367,368,369,490
%N A256577 Sum_{k>=0} (d_k)^(k+1)*10^k, where Sum_{k>=0} (d_k)*10^k is the decimal expansion of n.
%C A256577 a(n) = n when 0 <= n < 20 or 10^i <= n < 10^i + 20 for some i>1.
%C A256577 a(n) = n if and only if every digit of n (in base 10), except possibly the ones digit, is 0 or 1. Otherwise, n < a(n). - _Danny Rorabaugh_, Apr 02 2015
%H A256577 Michael De Vlieger, <a href="/A256577/b256577.txt">Table of n, a(n) for n = 0..10000</a>
%e A256577 a(19) = 1^2 * 10^1 + 9^1 * 10^0 = 19.
%e A256577 a(20) = 2^2 * 10^1 + 0^1 * 10^0 = 40.
%e A256577 a(40) = 4^2 * 10^1 + 0^1 * 10^0 = 160.
%e A256577 a(199) = 1^3 * 10^2 + 9^2 * 10^1 + 9^1 * 10^0 = 100 + 810 + 9 = 919.
%t A256577 Array[Total@ MapIndexed[#1^(#2)*10^(#2 - 1) & @@ {#1, First[#2]} &, Reverse@ IntegerDigits[#]] &, 71, 0] (* _Michael De Vlieger_, Nov 16 2022 *)
%o A256577 (PARI) vector(80, n, d = digits(n); sum(k=1, #d, d[k]^(#d-k+1)*10^(#d-k))) \\ _Michel Marcus_, Apr 09 2015
%Y A256577 Cf. A066566 (first 39 terms identical).
%Y A256577 Cf. A255073 (primes that remain prime, no carry).
%K A256577 base,nonn,easy
%O A256577 0,3
%A A256577 _Michael De Vlieger_, Apr 02 2015
%E A256577 Name and comments corrected by _Paul Tek_, Apr 11 2015