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A265310
Least positive k such that the product of divisors of n (A007955) divides k!.
1
1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 9, 13, 14, 10, 12, 17, 15, 19, 15, 14, 22, 23, 16, 15, 26, 15, 21, 29, 20, 31, 16, 22, 34, 14, 21, 37, 38, 26, 20, 41, 28, 43, 33, 15, 46, 47, 24, 21, 25, 34, 39, 53, 27, 22, 28, 38, 58, 59, 25, 61, 62, 21, 24, 26, 44, 67, 51, 46, 28, 71, 27, 73
OFFSET
1,2
COMMENTS
Conjecture: a(n) = n if and only if n is prime, 2*prime, 1, 8 or 9.
LINKS
MAPLE
A265310:= proc(n) local F, f, tau, a, p, k;
F:= ifactors(n)[2];
tau:= mul(1+f[2], f=F);
k:= 1;
for f in F do
a:= f[2]*tau/2;
p:= f[1];
while add(floor(k/p^j), j=1..ilog[p](k)) < a do k:= p*(1+floor(k/p)) od;
od;
k
end proc:
map(A265310, [$1..100]); # Robert Israel, Dec 07 2015
MATHEMATICA
Table[k = 1; While[! Divisible[k!, Times @@ Divisors@ n], k++]; k, {n, 73}] (* Michael De Vlieger, Dec 06 2015 *)
PROG
(PARI) a007955(n) = if(issquare(n, &n), n^numdiv(n^2), n^(numdiv(n)/2));
a(n) = {k=1; while(k, if(k! % a007955(n)==0, return(k)); k++)}
vector(100, n, a(n)) \\ Altug Alkan, Dec 06 2015
CROSSREFS
Cf. A007955.
Sequence in context: A327526 A121758 A121759 * A291576 A355221 A180613
KEYWORD
nonn
AUTHOR
Gionata Neri, Dec 06 2015
STATUS
approved