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A066460 a(n) is the least positive integer k such that k is a repdigit number in exactly n different bases B, where 1<B<k. 5

%I

%S 1,3,7,15,24,40,60,144,120,180,336,420,360,900,960,720,840,1260,1440,

%T 2340,1680,2880,3600,8190,2520,9072,9900,6300,6720,20592,5040,10920,

%U 7560,31320,98040,25920,10080,21420,177156,74256,15120,28560,20160

%N a(n) is the least positive integer k such that k is a repdigit number in exactly n different bases B, where 1<B<k.

%C All numbers n are repdigit in base 1 and in all bases greater than n, therefore we restrict the sequence to bases between 1 and n exclusively.

%H Giovanni Resta, <a href="/A066460/b066460.txt">Table of n, a(n) for n = 0..100</a>

%e a(4) = 24 since 24_10 = 44_5 = 33_7 = 22_11 = 11_23.

%t rp[n_, b_] := 1 == Length@ Union@ IntegerDigits[n, b]; c[1] = c[2] = 0; c[n_] := c[n] = Block[{q = Floor@Sqrt@n}, 1 + Length@ Select[Range[2, q], rp[n, #] &] + Length@ Select[Divisors[n] - 1, q < # <= n/2 && rp[n, #] &]]; a[n_] := Block[{k = 1}, While[c[k] != n, k++]; k]; Table[a[j], {j, 0, 30}] (* _Giovanni Resta_, Apr 07 2017 *)

%Y Cf. A066044.

%K nonn

%O 0,2

%A _Robert G. Wilson v_, Jan 02 2002

%E Edited by _John W. Layman_, Jan 16 2002

%E a(0) changed to 1 by _Giovanni Resta_, Apr 07 2017

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Last modified June 14 15:36 EDT 2021. Contains 345025 sequences. (Running on oeis4.)