OFFSET
1,1
COMMENTS
A256017(n) is the least integer k > n such that all divisors of n are exactly the first divisors of k in increasing order. a(n) is the ratio A256017(n)/n. This ratio is a prime number.
a(p)=p if p prime;
a(n)=2 if n is a power of 2;
a(n)=3 if n = 3, 6, 9, 18, 27, 54, 81, 162, 243, 486, 729, ... (A038754);
a(n)=5 if n = 5, 10, 15, 20, 25, 50, ... (A140730);
a(n)=7 if n = 7, 14, 21, 28, 35, 42, 49, 98, 147, 196, 245, ...
LINKS
Michel Lagneau, Table of n, a(n) for n = 1..10000
FORMULA
a(n) = A256017(n)/n.
MATHEMATICA
a[n_]:=If[n==1, 2, Block[{k= 2*n, f, d, m}, f = FactorInteger @n; If[1 == Length@f, f[[1, 1]]^(1 + f[[1, 2]]), d = Divisors@ n; m = Length@ d; While[ Take[ Divisors@ k, m] != d, k += n]; k]]]/n; Array[a, 100](* program from Giovanni Resta, adapted for this sequence. See A256017 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Michel Lagneau, Jun 01 2015
STATUS
approved