OFFSET
1,5
COMMENTS
n is prime iff a(n) = floor(n/2).
For n >= 2, a(n) is the number of integers of the form binomial(n-k-1, k-1)/k, k=1..floor(n/2). - Vladimir Shevelev, Aug 18 2013
LINKS
Peter J. C. Moses, Table of n, a(n) for n = 1..2000
FORMULA
For n >= 2, a(n) >= A000010(n)/2. Equality holds when n is odd prime.
EXAMPLE
In the fifth row, 5 and 5 are both multiples of 5, so a(5)=2.
MATHEMATICA
p[0]:=0; p[1]:=2; p[n_]:=p[n]=Expand[p[n-1] +x p[n-2]+1]; Flatten[{1, Table[Count[CoefficientList[p[n]/(n+1) , x], _Integer], {n, 50}]}] (* Peter J. C. Moses, Aug 20 2013 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Vladimir Shevelev, May 10 2010
EXTENSIONS
Definition shortened, more terms added by R. J. Mathar, Nov 01 2010
STATUS
approved