The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A245557 Irregular triangle read by rows: T(n,k) (n>=0, 0 <= k <= 2n) = number of triples (u,v,w) with entries in the range 0 to n which have some pair adding up to k and in which at least one of u,v,w is equal to n. 2
 1, 3, 6, 4, 3, 6, 15, 12, 7, 3, 6, 9, 24, 21, 18, 10, 3, 6, 9, 12, 33, 30, 27, 24, 13, 3, 6, 9, 12, 15, 42, 39, 36, 33, 30, 16, 3, 6, 9, 12, 15, 18, 51, 48, 45, 42, 39, 36, 19, 3, 6, 9, 12, 15, 18, 21, 60, 57, 54, 51, 48, 45, 42, 22 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS The sum of (left-justified) rows 0 through n gives row n of A245556. For example, the sum of rows 0 thru 2 is 7, 12, 19, 12, 7, which is the n=2 row of A245556. LINKS FORMULA T(n,k) = 3k (0 <= k <= n-1), T(n,k) = 12n-3k-3 (n <= k <= 2n-1), T(n,2n) = 3n+1. EXAMPLE Triangle begins: [1] [3, 6, 4] [3, 6, 15, 12, 7] [3, 6, 9, 24, 21, 18, 10] [3, 6, 9, 12, 33, 30, 27, 24, 13] [3, 6, 9, 12, 15, 42, 39, 36, 33, 30, 16] [3, 6, 9, 12, 15, 18, 51, 48, 45, 42, 39, 36, 19] [3, 6, 9, 12, 15, 18, 21, 60, 57, 54, 51, 48, 45, 42, 22] ... Example. Suppose n = 2. We find: triple count pair-sums 0  1  2  3  4                        ------------- 002      3     0,2     3     3 012      6     1,2,3      6  6  6 112      3     2,3           3  3 022      3     2,4           3     3 122      3     3,4              3  3 222      1     4                   1                        ------------- Totals:                3  6 15 12  7, which is row 2 of the triangle. MAPLE See A245556. CROSSREFS Partial sums of the rows gives A245556. Row sums are A082040. Sequence in context: A321872 A221363 A245943 * A197071 A231737 A140072 Adjacent sequences:  A245554 A245555 A245556 * A245558 A245559 A245560 KEYWORD nonn,tabf AUTHOR N. J. A. Sloane, Aug 04 2014 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified August 10 00:32 EDT 2022. Contains 356026 sequences. (Running on oeis4.)