A221533 a(n) is the number of integers of the form binomial(4*n^2 - k - 2, k - 1) / k, k=3, 4, ... , 2*n^2 - 2, n >= 2.
1, 9, 18, 33, 57, 60, 84, 141, 147, 187, 245, 265, 330, 417, 421, 430, 551, 620, 683, 837, 791, 865, 1056, 1044, 1182, 1288, 1278, 1506, 1737, 1677, 1685, 1983, 2097, 2228, 2517, 2433, 2423, 2780, 2926, 3079, 3253, 3216, 3563, 3733, 3713, 3872, 4249, 4318
Offset: 2
Keywords
Links
- Peter J. C. Moses, Table of n, a(n) for n = 2..301
Crossrefs
Cf. A177501.
Programs
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Mathematica
Table[Count[Table[Binomial[4*n^2-k-2,k-1]/k, {k,3,2*n^2-2}], Integer], {n, 2, 30}] (* _Peter J. C. Moses, Aug 17 2013 *)
Formula
If (2n-1, 2n+1) is a pair of twin primes, then a(n) = 2*n^2 - 2*n - 3.
Extensions
More terms from Peter J. C. Moses, Aug 17 2013