A136527 Triangle read by rows: T(n,k) = greatest common divisor of n-th and k-th composite number, 1<=k<=n.

4, 2, 6, 4, 2, 8, 1, 3, 1, 9, 2, 2, 2, 1, 10, 4, 6, 4, 3, 2, 12, 2, 2, 2, 1, 2, 2, 14, 1, 3, 1, 3, 5, 3, 1, 15, 4, 2, 8, 1, 2, 4, 2, 1, 16, 2, 6, 2, 9, 2, 6, 2, 3, 2, 18, 4, 2, 4, 1, 10, 4, 2, 5, 4, 2, 20, 1, 3, 1, 3, 1, 3, 7, 3, 1, 3, 1, 21, 2, 2, 2, 1, 2, 2, 2, 1, 2, 2, 2, 1, 22, 4, 6, 8, 3, 2, 12, 2, 3, 8, 6, 4, 3, 2, 24

Offset: 1

Author

Reinhard Zumkeller, Jan 03 2008

Keywords

• nonn
• tabl

Examples

			4;
2, 6;
4, 2, 8;
1, 3, 1, 9;
2, 2, 2, 1, 10;
...
		

Crossrefs

Cf. A002808, A050873, A073783.

Programs

Mathematica

nmax = 14;
A002808 = Select[Range[FindRoot[n == nmax + PrimePi[n] + 1, {n, nmax, 2nmax}][[1, 2]] // Ceiling], CompositeQ];
T[n_, k_] := GCD[A002808[[n]], A002808[[k]]];
Table[T[n, k], {n, 1, nmax}, {k, 1, n}] // Flatten (* Jean-François Alcover, Nov 15 2021 *)

Formula

T(n,k) = A050873(A002808(n),A002808(k));

A073783(n) = T(n-1,n) for n>1;

A002808(n) = T(n,n).