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 A117828 #23 Nov 07 2016 11:12:33 %S A117828 1,5,9,13,35,57,79,101,105,505,509,909,913,323,327,727,731,141,145, %T A117828 545,549,949,953,363,367,767,771,181,185,585,589,989,993,403,308,807, %U A117828 712,221,126,625,530,39,97,83,42,28,86,72,31,17,75,61,20,6,10,5,9,13,35,57,79,101,105,505,509,909,913,323,327,727,731 %N A117828 Start with 1 and repeatedly reverse the decimal digits and add 4 to get the next term. %H A117828 N. J. A. Sloane and others, <a href="/wiki/Sequences_of_RADD_type">Sequences of RADD type</a>, OEIS wiki. %H A117828 <a href="/index/Rec#order_54">Index entries for linear recurrences with constant coefficients</a>, signature (0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1). %F A117828 After one step enters a cycle of length 54: see A117827, A117830. %p A117828 read transforms; t1:=[1]; for n from 1 to 80 do t1:=[op(t1),4+digrev(t1[n])]; od: # _N. J. A. Sloane_ %t A117828 f[n_] := 4 + FromDigits@ Reverse@ IntegerDigits@n; NestList[ f@# &, 1, 57] (* and *) %t A117828 (* to view the cycle *) NestWhileList[ f@# &, 1, UnsameQ, All] (* _Robert G. Wilson v_, May 09 2006 *) %o A117828 (PARI) a(n)=if(n>1, my(t=6); for(k=1,n%54, t=fromdigits(Vecrev(digits(t)))+4); t, 1) \\ _Charles R Greathouse IV_, Nov 07 2016 %Y A117828 Cf. A117827, A117829, A117830. %K A117828 nonn,base,easy %O A117828 1,2 %A A117828 Luc Stevens (lms022(AT)yahoo.com), Apr 06 2006