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%I #29 Jan 21 2022 05:07:37
%S 0,1,2,3,4,6,12,18,24,31,62,93,124,156,312,468,624,781,1562,2343,3124,
%T 3906,7812,11718,15624,19531,39062,58593,78124,97656,195312,292968,
%U 390624,488281,976562,1464843,1953124,2441406,4882812,7324218,9765624
%N Numbers that are repdigits in base 5.
%H Vincenzo Librandi, <a href="/A048330/b048330.txt">Table of n, a(n) for n = 0..400</a>
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/Repdigit.html">Repdigit</a>.
%F 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
%F Sum_{n>=1} 1/a(n) = (25/3) * A248722 = 2.51444877998310381623... - _Amiram Eldar_, Jan 21 2022
%e 12_10 = 22_5, 18_10 = 33_5, 7812_10 = 222222_5.
%t Union[Flatten[Table[FromDigits[PadRight[{}, n, d], 5], {n, 0, 40}, {d, 4}]]] (* _Vincenzo Librandi_, Feb 06 2014 *)
%o (Magma) [0] cat [k:k in [1..10^7]| #Set(Intseq(k,5)) eq 1]; // _Marius A. Burtea_, Oct 11 2019
%Y Cf. A010785, A033018, A028987, A028988, A248722.
%K nonn,base
%O 0,3
%A _Patrick De Geest_, Feb 15 1999
%E Offset changed from 1 to 0 by _Vincenzo Librandi_, Feb 06 2014
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