OFFSET
0,3
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 0..400
Eric Weisstein's World of Mathematics, Repdigit.
FORMULA
Conjecture: G.f.: x*(1+2*x+3*x^2+4*x^3) / ( (x-1)*(1+x)*(x^2+1)*(5*x^4-1) ) with a(n) = 6*a(n-4) - 5*a(n-8). - R. J. Mathar, Mar 15 2015
Sum_{n>=1} 1/a(n) = (25/3) * A248722 = 2.51444877998310381623... - Amiram Eldar, Jan 21 2022
EXAMPLE
12_10 = 22_5, 18_10 = 33_5, 7812_10 = 222222_5.
MATHEMATICA
Union[Flatten[Table[FromDigits[PadRight[{}, n, d], 5], {n, 0, 40}, {d, 4}]]] (* Vincenzo Librandi, Feb 06 2014 *)
PROG
(Magma) [0] cat [k:k in [1..10^7]| #Set(Intseq(k, 5)) eq 1]; // Marius A. Burtea, Oct 11 2019
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Patrick De Geest, Feb 15 1999
EXTENSIONS
Offset changed from 1 to 0 by Vincenzo Librandi, Feb 06 2014
STATUS
approved