OFFSET
0,2
COMMENTS
For n > 0, a(n) is of the form 2^k*primorial(d) where d is a divisor of n and k = n / d - d + 1. a(n) is never 0 since A307409(2^(n+1)) = n. - Andrew Howroyd, Nov 04 2019
LINKS
Andrew Howroyd, Table of n, a(n) for n = 0..1000
FORMULA
From Andrew Howroyd, Nov 03 2019: (Start)
a(p) = 2^(p + 1) for odd prime p.
a(n) = min_{d|n, d<=n/d+1} 2^(n/d-d+1)*A002110(d) for n > 0. (End)
EXAMPLE
The sequence of terms together with their prime signatures begins:
1: ()
4: (2)
6: (1,1)
16: (4)
12: (2,1)
64: (6)
24: (3,1)
256: (8)
48: (4,1)
60: (2,1,1)
96: (5,1)
4096: (12)
120: (3,1,1)
16384: (14)
384: (7,1)
240: (4,1,1)
420: (2,1,1,1)
MATHEMATICA
dat=Table[(PrimeOmega[n]-1)*PrimeNu[n], {n, 1000}];
Table[Position[dat, i][[1, 1]], {i, First[Split[Union[dat], #2==#1+1&]]}]
PROG
(PARI) a(n)={if(n<1, 1, my(m=oo); fordiv(n, d, if(d<=n/d+1, m=min(m, 2^(n/d-d+1)*vecprod(primes(d))))); m)} \\ Andrew Howroyd, Nov 04 2019
CROSSREFS
KEYWORD
nonn
AUTHOR
Gus Wiseman, Nov 02 2019
EXTENSIONS
Terms a(23) and beyond from Andrew Howroyd, Nov 03 2019
STATUS
approved