OFFSET
1,1
EXAMPLE
For k=2,3,4,5,6, we have the following factorizations of k! over distinct terms of A050376: 2!=2, 3!=2*3, 4!=2*3*4, 5!=2*3*4*5, 6!=5*9*16.
Therefore, a(1)=4, a(2)=6.
MATHEMATICA
f[n_] := DigitCount[n, 2, 1] - Mod[n, 2]; nb[n_] := Total@(f/@ FactorInteger[n][[;; , 2]]); a[n_] := (k=1; While[nb[k!] < n, k++]; k); Array[a, 60] (* Amiram Eldar, Dec 16 2018 from the PARI code *)
PROG
(PARI) nb(n) = {my(f = factor(n)); sum(k=1, #f~, hammingweight(f[k, 2]) - (f[k, 2] % 2)); }
a(n) = {my(k=1); while (nb(k!) < n, k++); k; } \\ Michel Marcus, Dec 16 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
Vladimir Shevelev, Apr 16 2014
EXTENSIONS
More terms from Michel Marcus, Dec 16 2018
STATUS
approved