A173662 - OEIS

%I #17 Jun 28 2024 21:10:37

%S 0,2,0,1,3,0,2,4,1,0,2,2,5,4,0,3,3,6,5,1,0,1,3,3,1,7,6,0,2,4,4,2,8,7,

%T 1,0,1,1,7,5,11,10,4,3,0,2,2,8,6,12,11,5,4,1,0,1,3,6,3,5,3,12,11,8,7,

%U 0,2,4,7,4

%N Triangle read by rows: T(n,k) = semiprime(n) mod semiprime(k), 1 <= k <= n.

%C Row sums are 0, 2, 4, 7, 13, 18, 28, ...

%e Triangle begins:

%e   0,

%e   2,0;

%e   1,3,0;

%e   2,4,1,0;

%e   2,2,5,4,0;

%e   3,3,6,5,1,0;

%e   1,3,3,1,7,6,0;

%e   2,4,4,2,8,7,1,0;

%t SemiprimeQ[n_Integer] := If[Abs[n]<2, False, (2==Plus@@Transpose[FactorInteger[Abs[n]]][[2]])]; sp = Select[Range[100], SemiprimeQ]; Flatten[Table[Mod[sp[[n]], sp[[Range[n]]]], {n,Length[sp]}]]

%Y Cf. A001358, A173655.

%K nonn,tabl,easy

%O 1,2

%A _Juri-Stepan Gerasimov_, Nov 28 2010

%E 46th term corrected by _D. S. McNeil_, Nov 24 2010