A214426 Numbers n palindromic in exactly four bases b, 2 <= b <= 10.

8, 121, 373, 786435

Offset: 1

Author

T. D. Noe, Jul 18 2012

Keywords

• nonn
• base
• hard

Comments

Searched up to 10^18. Rick Regan mentions these four numbers, also found by Bill Beckmann, at the end of his webpage. - T. D. Noe, Aug 18 2012

Examples

			8 is palindromic in bases 3, 7, 9, and 10.
121 is palindromic in bases 3, 7, 8, and 10.
373 is palindromic in bases 4, 7, 9, and 10.
786435 is palindromic in bases 2, 4, 7, and 8.
		

Links

• Rick Regan, Finding numbers that are palindromic in multiple bases

Crossrefs

Cf. A050813, A214423, A214424, A214425 (palindromic in 0-3 bases).

Programs

Mathematica

n = -1; t = {}; While[Length[t] < 4, n++; If[Count[Table[s = IntegerDigits[n, m]; s == Reverse[s], {m, 2, 10}], True] == 4, AppendTo[t, n]]]; t

Formula

A050812(n) = 4.