OFFSET
4,3
COMMENTS
For all values of a(n), where a(n) is not equal to A001405(n), n is either: a prime, a power of a prime, a prime +1 or a power of a prime +1.
MATHEMATICA
a[n_] := Binomial[n, Floor[n/2]]/GCD @@ Binomial[n, Range[2, n/2]]; Array[a, 30, 4] (* Amiram Eldar, Oct 24 2019 *)
PROG
(PARI) a(n) = binomial(n, n\2)/gcd(vector((n+1)\2-1, k, binomial(n, k+1))); \\ Michel Marcus, Oct 24 2019
CROSSREFS
KEYWORD
nonn
AUTHOR
Joel Kaufmann, Oct 24 2019
STATUS
approved