A140869 Triangle read by rows where T(m,n) = floor((2mn+m+n-2)/2), m >= n >= 1.

1, 2, 5, 4, 7, 11, 5, 10, 14, 19, 7, 12, 18, 23, 29, 8, 15, 21, 28, 34, 41, 10, 17, 25, 32, 40, 47, 55, 11, 20, 28, 37, 45, 54, 62, 71, 13, 22, 32, 41, 51, 60, 70, 79, 89, 14, 25, 35, 46, 56, 67, 77, 88, 98, 109, 16, 27, 39, 50, 62, 73, 85, 96, 108, 119, 131, 17, 30, 42, 55, 67, 80, 92, 105, 117, 130, 142, 155

Offset

1,2

Comments

Conjecture: If h does not belong to the sequence, then 4*h+5 is prime. - Vincenzo Librandi, Nov 18 2012

First column: A001651; second column: A047215; third column: A047345. - Vincenzo Librandi, Nov 18 2012

Links

Vincenzo Librandi, Rows n = 1..100, flattened

Example

Triangle begins:
1;
2,  5;
4,  7,  11;
5,  10, 14, 19;
7,  12, 18, 23, 29;
8,  15, 21, 28, 34, 41;
10, 17, 25, 32, 40, 47, 55; etc.

Mathematica

Flatten[Table[Floor[(2*n*m+m+n-2)/2], {n, 1, 10}, {m, n}]] (* Vladimir Joseph Stephan Orlovsky, Feb 03 2012 *)

Prog

(Magma) [Floor(((2*n*k+n+k-2)/2)): k in [1..n], n in [1..11]]; // Vincenzo Librandi, Nov 18 2012

Crossrefs

Cf. A002327, A153085, A001651, A047215, A047345.

Sequence in context: A036237 A015948 A119733 * A111570 A057954 A155896

Adjacent sequences: A140866 A140867 A140868 * A140870 A140871 A140872

Keyword

nonn,tabl,easy

Author

Vincenzo Librandi, Jan 16 2009

Status

approved