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.

1, 3, 7, 15, 24, 40, 60, 144, 120, 180, 336, 420, 360, 900, 960, 720, 840, 1260, 1440, 2340, 1680, 2880, 3600, 8190, 2520, 9072, 9900, 6300, 6720, 20592, 5040, 10920, 7560, 31320, 98040, 25920, 10080, 21420, 177156, 74256, 15120, 28560, 20160

Offset

0,2

Comments

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.

Links

Giovanni Resta, Table of n, a(n) for n = 0..100

Example

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

Mathematica

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 *)

Crossrefs

Cf. A066044.

Sequence in context: A375704 A001213 A066044 * A114221 A289828 A226471

Adjacent sequences: A066457 A066458 A066459 * A066461 A066462 A066463

Keyword

nonn

Author

Robert G. Wilson v, Jan 02 2002

Extensions

Edited by John W. Layman, Jan 16 2002

a(0) changed to 1 by Giovanni Resta, Apr 07 2017

Status

approved