A073766 a(n) = binomial(composite(n+1), composite(n)) = binomial(A002808(n+1), A002808(n)).

15, 28, 9, 10, 66, 91, 15, 16, 153, 190, 21, 22, 276, 25, 26, 27, 28, 435, 496, 33, 34, 35, 36, 703, 39, 40, 861, 946, 45, 46, 1128, 49, 50, 51, 52, 1431, 55, 56, 57, 58, 1770, 1891, 63, 64, 65, 66, 2278, 69, 70, 2556, 2701, 75, 76, 77, 78, 3160, 81, 82, 3486, 85

Offset: 1

Author

Labos Elemer, Aug 09 2002

Keywords

• nonn

Comments

a(n) equals either composite(n+1) or composite(w)+1 or binomial(c,2) for some composite number c.

Links

• Michael De Vlieger, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A002808.

Programs

Mathematica

Block[{f}, f[n_] := FixedPoint[n + PrimePi@ # + 1 &, n + PrimePi[n] + 1]; Array[Binomial[f[# + 1], f[#]] &, 10^4]] (* Michael De Vlieger, Nov 05 2020 *)

PARI

lista(nn) = {my(prec  = 0); forcomposite(c=1, nn, if (prec, print1(binomial(c, prec), ", ")); prec = c;);} \\ Michel Marcus, Mar 26 2020

Extensions

Edited by Michael De Vlieger, Nov 05 2020