OFFSET
1,2
LINKS
David A. Corneth, Table of n, a(n) for n = 1..10000
FORMULA
If a solution exists, a(n) is the concatenation of prime factors with repetitions and in order of magnitude, otherwise a(n)=0.
MATHEMATICA
Array[If[#[[-1, 1]] > 7, 0, FromDigits@ Reverse@ Flatten@ Map[ConstantArray[#1, #2] & @@ # &, #]] &@ FactorInteger@ # &, 69] /. 1 -> 0 (* Michael De Vlieger, Dec 08 2018 *)
PROG
(PARI) a(n) = {my(res = []); for(i=2, 9, v = valuation(n, i); if(v > 0, res = concat(vector(v, j, i), res); n/=i^v)); if(n==1, fromdigits(res), 0)} \\ David A. Corneth, Jul 31 2017
CROSSREFS
KEYWORD
base,nonn
AUTHOR
Labos Elemer, Feb 19 2002
EXTENSIONS
a(36) corrected by David A. Corneth, Jul 31 2017
STATUS
approved