OFFSET
0,3
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 0..300
Eric Weisstein's World of Mathematics, Repdigit.
Index entries for linear recurrences with constant coefficients, signature (0,0,5,0,0,-4).
FORMULA
G.f.: x*(1+2*x+3*x^2) / ( (x-1)*(4*x^3-1)*(1+x+x^2) ) with a(n) = 5*a(n-3) - 4*a(n-6). - R. J. Mathar, Mar 15 2015
Sum_{n>=1} 1/a(n) = (11/2) * A248721 = 2.31603727318383077512... - Amiram Eldar, Jan 21 2022
EXAMPLE
10_10 = 22_4, 15_10 = 33_4, 5461_10 = 1111111_4.
MAPLE
a:= n-> (1+irem(n+2, 3))*(4^iquo(n+2, 3)-1)/3:
seq(a(n), n = 0..45);
MATHEMATICA
Union[Flatten[Table[FromDigits[PadRight[{}, n, d], 4], {n, 0, 40}, {d, 3}]]](* Vincenzo Librandi, Feb 06 2014 *)
LinearRecurrence[{0, 0, 5, 0, 0, -4}, {0, 1, 2, 3, 5, 10}, 40] (* Harvey P. Dale, Jul 11 2023 *)
PROG
(Magma) [0] cat [k:k in [1..10^7]| #Set(Intseq(k, 4)) eq 1]; // Marius A. Burtea, Oct 11 2019
CROSSREFS
KEYWORD
nonn,base,easy
AUTHOR
Patrick De Geest, Feb 15 1999
STATUS
approved