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%I #7 Nov 15 2021 04:37:20
%S 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,
%T 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,
%U 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
%N Triangle read by rows: T(n,k) = greatest common divisor of n-th and k-th composite number, 1<=k<=n.
%F T(n,k) = A050873(A002808(n),A002808(k));
%F A073783(n) = T(n-1,n) for n>1;
%F A002808(n) = T(n,n).
%e 4;
%e 2, 6;
%e 4, 2, 8;
%e 1, 3, 1, 9;
%e 2, 2, 2, 1, 10;
%e ...
%t nmax = 14;
%t A002808 = Select[Range[FindRoot[n == nmax + PrimePi[n] + 1, {n, nmax, 2nmax}][[1, 2]] // Ceiling], CompositeQ];
%t T[n_, k_] := GCD[A002808[[n]], A002808[[k]]];
%t Table[T[n, k], {n, 1, nmax}, {k, 1, n}] // Flatten (* _Jean-François Alcover_, Nov 15 2021 *)
%Y Cf. A002808, A050873, A073783.
%K nonn,tabl
%O 1,1
%A _Reinhard Zumkeller_, Jan 03 2008
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