A109903 Let c = composite(n) & p = prime(n); a(n) = binomial( max(c,p), min(c,p) ).

6, 20, 56, 36, 11, 13, 680, 3876, 245157, 34597290, 84672315, 12875774670, 244662670200, 800472431850, 14833897694226, 973469712824056, 48402641245296107, 191724747789809255, 9989690752182277136

Offset

1,1

Comments

11 and 13 are the only prime terms. For a(7) onwards sequence is monotonically increasing.

Links

Table of n, a(n) for n=1..19.

Example

a(3) = C(8,5) = 56, a(8) = C(19,15) =3876.

Mathematica

Composite[ n_Integer ] := Block[{k = n + PrimePi[ n ] + 1}, While[ k != n + PrimePi[ k ] + 1, k++ ]; k]; f[n_] := Block[{a = Sort[{Composite[n], Prime[n]}]}, Binomial[Last[a], First[a]]]; Table[ f[n], {n, 19}] (* Robert G. Wilson v, Jul 16 2005 *)

Crossrefs

Sequence in context: A213589 A152959 A328681 * A323640 A249406 A220020

Adjacent sequences: A109900 A109901 A109902 * A109904 A109905 A109906

Keyword

easy,nonn

Author

Amarnath Murthy, Jul 14 2005

Extensions

More terms from Robert G. Wilson v, Jul 16 2005

Status

approved