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A048330
Numbers that are repdigits in base 5.
4
0, 1, 2, 3, 4, 6, 12, 18, 24, 31, 62, 93, 124, 156, 312, 468, 624, 781, 1562, 2343, 3124, 3906, 7812, 11718, 15624, 19531, 39062, 58593, 78124, 97656, 195312, 292968, 390624, 488281, 976562, 1464843, 1953124, 2441406, 4882812, 7324218, 9765624
OFFSET
0,3
LINKS
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