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

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%I A151969 #4 Jan 28 2016 09:52:49
%S A151969 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,
%T A151969 32,32,32,32,32,32,32,40,40,40,40,40,40,40,40,50,50,50,50,50,50,50,50,
%U A151969 50,50,64,64,64,64,64,64,64,64,64,64,64,64,64,64,80,80,80,80,80
%N A151969 a(n) = smallest integer >= n which has only prime factors 2 and 5.
%H A151969 Harvey P. Dale, <a href="/A151969/b151969.txt">Table of n, a(n) for n = 1..1000</a>
%t A151969 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 *)
%o A151969 (R) f <- function(n) nextn(n, factors = c(2,5))
%o A151969 a <- matrix(1:256,ncol=1)
%o A151969 apply(a,1,f)
%Y A151969 Cf. A130916, A134361, A151970.
%K A151969 nonn
%O A151969 1,2
%A A151969 _N. J. A. Sloane_, Aug 23 2009