OFFSET
1,2
FORMULA
For a fixed m, generating function is 1/(1-2*x+x^(m+1)) - 1/(1-x).
T(n,m) = Sum_{i=0..floor(n/(m+1))} binomial(n-mi, i)*(-1)^i*2^(n-(m+1)i) - 1.
T(n,m) = 2^m - 1 + Sum_{j=m+1..n} A126198(j,m).
EXAMPLE
Triangle begins:
1;
2, 3;
3, 6, 7;
4, 11, 14, 15;
5, 19, 27, 30, 31;
6, 32, 51, 59, 62, 63;
7, 53, 95, 115, 123, 126, 127;
...
Could also be extended to a square array:
1, 1, 1, 1, 1, 1, 1, ...
2, 3, 3, 3, 3, 3, 3, ...
3, 6, 7, 7, 7, 7, 7, ...
4, 11, 14, 15, 15, 15, 15, ...
5, 19, 27, 30, 31, 31, 31, ...
6, 32, 51, 59, 62, 63, 63, ...
7, 53, 95, 115, 123, 126, 127, ...
PROG
(PARI) { T(n, m) = sum(i=0, n\(m+1), binomial(n-m*i, i) * (-1)^i * 2^(n-(m+1)*i) ) - 1 }
CROSSREFS
KEYWORD
nonn,tabl
AUTHOR
Max Alekseyev, Nov 17 2010
STATUS
approved