OFFSET
1,1
COMMENTS
Same as the number of distinct prime factors in (2n^2+2n)!/(n^2)!. The plot appears nearly linear.
LINKS
T. D. Noe, Table of n, a(n) for n=1..10000
EXAMPLE
The numbers between 4 and 9 have factorizations 5, 2*3, 7, 2^4, which use primes 2, 3, 5 and 7. Hence a(2)=4.
MATHEMATICA
Table[a=n^2; b=a+2*n; Sum[Sign[Quotient[b, p]-Quotient[a, p]], {p, Prime[Range[PrimePi[b]]]}], {n, 100}]
CROSSREFS
KEYWORD
nonn
AUTHOR
T. D. Noe, Aug 09 2008
STATUS
approved