A151969 a(n) = smallest integer >= n which has only prime factors 2 and 5.

1, 2, 4, 4, 5, 8, 8, 8, 10, 10, 16, 16, 16, 16, 16, 16, 20, 20, 20, 20, 25, 25, 25, 25, 25, 32, 32, 32, 32, 32, 32, 32, 40, 40, 40, 40, 40, 40, 40, 40, 50, 50, 50, 50, 50, 50, 50, 50, 50, 50, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 80, 80, 80, 80, 80

Offset

1,2

Links

Harvey P. Dale, Table of n, a(n) for n = 1..1000

Mathematica

Module[{upto=100, pwr, f25}, pwr=Ceiling[Log[2, upto]]; f25=Select[ Sort[ Flatten[ Table[Times@@@Union[Sort/@Tuples[{2, 5}, n]], {n, 0, pwr}]]], #<= upto&]; Table[SelectFirst[f25, #>i&], {i, 0, upto-1}]] (* The program uses the SelectFirst function from Mathematica version 10 *) (* Harvey P. Dale, Jan 28 2016 *)

Prog

(R) f <- function(n) nextn(n, factors = c(2, 5))
a <- matrix(1:256, ncol=1)
apply(a, 1, f)

Crossrefs

Cf. A130916, A134361, A151970.

Sequence in context: A084824 A344710 A184615 * A261393 A366541 A327629

Adjacent sequences: A151966 A151967 A151968 * A151970 A151971 A151972

Keyword

nonn

Author

N. J. A. Sloane, Aug 23 2009

Status

approved