OFFSET
1,1
COMMENTS
A number m belongs to this sequence if and only if it is odd and composite.
First column: A016945(n, n>=1), second column: A017329(n, n>=2), third column: A147587(n, n>=3). - Vincenzo Librandi, Nov 20 2012
The number of occurrences of m corresponds to the number of nontrivial factorizations of m, i.e., A072670(m-1). - Daniel Forgues, Apr 22 2014
LINKS
Vincenzo Librandi, Rows n = 1..100, flattened
OEIS Wiki, Odd composites
FORMULA
T(n, k) = A144562(n,k)*2+3 read by rows. (Was old name.)
T(n, k) = 2*A083487(n, k)+1. - Daniel Forgues, Sep 20 2011
EXAMPLE
Triangle begins:
9;
15, 25;
21, 35, 49;
27, 45, 63, 81;
33, 55, 77, 99, 121;
39, 65, 91, 117, 143, 169;
45, 75, 105, 135, 165, 195, 225;
51, 85, 119, 153, 187, 221, 255, 289;
57, 95, 133, 171, 209, 247, 285, 323, 361;
63, 105, 147, 189, 231, 273, 315, 357, 399, 441; etc.
Number of occurrences:
63 = 9*7 = 21*3 has two nontrivial factorizations, thus occurs twice.
MATHEMATICA
t[n_, k_]:= 4 n*k + 2n + 2k + 1; Table[t[n, k], {n, 15}, {k, n}]//Flatten (* Vincenzo Librandi, Nov 20 2012 *)
PROG
(Magma) [4*n*k + 2*n + 2*k + 1: k in [1..n], n in [1..11]]; // Vincenzo Librandi, Nov 20 2012
CROSSREFS
KEYWORD
AUTHOR
Vincenzo Librandi, Nov 24 2010
STATUS
approved