A088323 Number of numbers b>1 such that n is a repunit in base b representation.

0, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 2, 1, 2, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 3, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1

Offset

2,6

Comments

is a(n) < 4 ?;

n>2: a(n) > 0 as n = (n-1)^1 + (n-1)^0.

a(A119598(n)) > 3; a(A053696(n)) > 2; a(A085104(n)) > 2. - Reinhard Zumkeller, Jan 22 2014

Links

Reinhard Zumkeller, Table of n, a(n) for n = 2..10000

Eric Weisstein's World of Mathematics, Repunit

Example

a(31)=3: 31 = 2^4+2^3+2^2+2^1+2^0 = 5^2+5^1+5^0 = 30^1+30^0.

Prog

(Haskell)
a088323 n = sum $ map (f n) [2 .. n-1] where
   f x b = if x == 0 then 1 else if d /= 1 then 0 else f x' b
                                 where (x', d) = divMod x b
-- Reinhard Zumkeller, Jan 22 2014

Crossrefs

Cf. A000225, A003462, A002275, A068953.

Sequence in context: A338160 A336137 A371735 * A003652 A071625 A331592

Adjacent sequences: A088320 A088321 A088322 * A088324 A088325 A088326

Keyword

nonn,base

Author

Reinhard Zumkeller, Nov 06 2003

Extensions

Example corrected by Reinhard Zumkeller, Jan 22 2014

Status

approved