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A214426
Numbers n palindromic in exactly four bases b, 2 <= b <= 10.
6
8, 121, 373, 786435
OFFSET
1,1
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
FORMULA
A050812(n) = 4.
EXAMPLE
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.
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
CROSSREFS
Cf. A050813, A214423, A214424, A214425 (palindromic in 0-3 bases).
Sequence in context: A034669 A375419 A000848 * A281833 A299077 A298997
KEYWORD
nonn,base,hard
AUTHOR
T. D. Noe, Jul 18 2012
STATUS
approved