A128893 (1/p)*(binomial(2*p,p)+2*(p-1)), where p = n-th prime.

4, 8, 52, 492, 64132, 800048, 137270956, 1860277044, 357975249028, 1036802293087624, 15013817846943908, 47192717955016924592, 10360599532897359064120, 154361699651715243559788, 34589385964790856394651396, 118349529407778329236413352408, 412825418773807104132857739017404

Offset

1,1

Comments

For p odd, this is the number of p-element subsets of {1, 2, ..., 2p} whose sum is divisible by p.

References

R. Honsberger, Mathematical Chestnuts from Around the World, MAA, 2001; see p. 220-223.

Links

Table of n, a(n) for n=1..17.

StackExchange, Easy number theory problem, Mar 25 2018

Mathematica

(1/# (Binomial[2#, #]+2(#-1)))&/@Prime[Range[30]] (* Harvey P. Dale, Oct 22 2011 *)

Crossrefs

Sequence in context: A189314 A358791 A215746 * A214603 A192508 A231601

Adjacent sequences: A128890 A128891 A128892 * A128894 A128895 A128896

Keyword

nonn

Author

N. J. A. Sloane, Jul 23 2008

Status

approved