A203533 -id:A203533 - cp's OEIS frontend

A203530 a(n) = Product_{1 <= i < j <= n} (c(i) + c(j)); c = A002808 = composite numbers.

1, 10, 1680, 5569200, 426645273600, 1135354270482432000, 129053267560513803386880000, 556394398742051964595520667648000000, 99449133623220179596974346585642106880000000000

Offset: 1

Clark Kimberling, Jan 03 2012

nonn

Each term divides its successor, as in A203530.
It is conjectured that each term is divisible by the corresponding superfactorial, A000178(n); as in A203533.
See A093883 for a guide to related sequences.

Cf. A002808, A203418, A203532, A203533.

c:= proc(n) option remember; local k; if n=1 then 4
      else for k from 1+c(n-1) while isprime(k) do od; k fi
    end:
a:= n-> mul(mul(c(i)+c(j), i=1..j-1), j=2..n):
seq(a(n), n=1..10);  # Alois P. Heinz, Jul 23 2017

t = Table[If[PrimeQ[k], 0, k], {k, 1, 100}];
composite = Rest[Rest[Union[t]]]       (* A002808 *)
f[j_] := composite[[j]]; z = 20;
v[n_] := Product[Product[f[k] + f[j], {j, 1, k - 1}], {k, 2, n}]
d[n_] := Product[(i - 1)!, {i, 1, n}]  (* A000178 *)
Table[v[n], {n, 1, z}]                 (* A203530 *)
Table[v[n + 1]/v[n], {n, 1, z - 1}]    (* A203532 *)
Table[v[n]/d[n], {n, 1, 20}]           (* A203533 *)

Name edited by Alois P. Heinz, Jul 23 2017

A203532 v(n+1)/v(n), where v=A203530.

Original entry on oeis.org

10, 168, 3315, 76608, 2661120, 113667840, 4311354600, 178738560000, 11178747740160, 791853627801600, 44783640216315000, 2693449157020876800, 246209683227475968000, 17126298576096297588000, 1253392853589570355200000

Offset: 1

Clark Kimberling, Jan 03 2012

nonn

Cf. A203530, A203532, A002808, A093883, A203419.

t = Table[If[PrimeQ[k], 0, k], {k, 1, 100}];
composite = Rest[Rest[Union[t]]]       (* A002808 *)
f[j_] := composite[[j]]; z = 20;
v[n_] := Product[Product[f[k] + f[j], {j, 1, k - 1}], {k, 2, n}]
d[n_] := Product[(i - 1)!, {i, 1, n}]  (* A000178 *)
Table[v[n], {n, 1, z}]                 (* A203530 *)
Table[v[n + 1]/v[n], {n, 1, z - 1}]    (* A203532 *)
Table[v[n]/d[n], {n, 1, 20}]           (* A203533 *)

cp's OEIS Frontend

A203530 a(n) = Product_{1 <= i < j <= n} (c(i) + c(j)); c = A002808 = composite numbers.

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