OFFSET
1,216
LINKS
FORMULA
EXAMPLE
For n = 8 = 2^3, there is one exponent that is exactly 3, thus a(8) = 1.
For n = 216 = 2^3 * 3^3 there are two exponents that are exactly 3, thus a(216) = 2.
For n = 432 = 2^4 * 3^3, there is one exponent that is exactly 3, thus a(432) = 1.
MATHEMATICA
Array[Total@ Map[Boole[# == 3] &, FactorInteger[#][[All, -1]]] &, 120] (* Michael De Vlieger, Nov 29 2017 *)
Count[FactorInteger[#][[All, 2]], 3]&/@Range[120] (* Harvey P. Dale, Apr 13 2019 *)
PROG
(Scheme, with memoization-macro definec)
(PARI) a(n) = vecsum(apply(x->(x==3), factor(n)[, 2])); \\ Michel Marcus, Jul 25 2022
CROSSREFS
KEYWORD
nonn
AUTHOR
Antti Karttunen, Nov 29 2017
STATUS
approved