%I #15 Nov 05 2020 19:27:12

%S 15,28,9,10,66,91,15,16,153,190,21,22,276,25,26,27,28,435,496,33,34,

%T 35,36,703,39,40,861,946,45,46,1128,49,50,51,52,1431,55,56,57,58,1770,

%U 1891,63,64,65,66,2278,69,70,2556,2701,75,76,77,78,3160,81,82,3486,85

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

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

%H Michael De Vlieger, <a href="/A073766/b073766.txt">Table of n, a(n) for n = 1..10000</a>

%t 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 *)

%o (PARI) lista(nn) = {my(prec = 0); forcomposite(c=1, nn, if (prec, print1(binomial(c, prec), ", ")); prec = c;);} \\ _Michel Marcus_, Mar 26 2020

%Y Cf. A002808.

%K nonn

%O 1,1

%A _Labos Elemer_, Aug 09 2002

%E Edited by _Michael De Vlieger_, Nov 05 2020