login
A126150
Symmetric triangle, read by rows of 2*n+1 terms, similar to triangle A008301.
5
1, 1, 4, 1, 6, 24, 36, 24, 6, 96, 384, 636, 744, 636, 384, 96, 2976, 11904, 20256, 26304, 28536, 26304, 20256, 11904, 2976, 151416, 605664, 1042056, 1407024, 1650456, 1736064, 1650456, 1407024, 1042056, 605664, 151416, 11449296, 45797184
OFFSET
0,3
FORMULA
Sum_{k=0,2n} (-1)^k*C(2n,k)*T(n,k) = (-6)^n.
EXAMPLE
Triangle begins:
1;
1, 4, 1;
6, 24, 36, 24, 6;
96, 384, 636, 744, 636, 384, 96;
2976, 11904, 20256, 26304, 28536, 26304, 20256, 11904, 2976;
151416, 605664, 1042056, 1407024, 1650456, 1736064, 1650456, 1407024, 1042056, 605664, 151416; ...
If we write the triangle like this:
.......................... ....1;
................... ....1, ....4, ....1;
............ ....6, ...24, ...36, ...24, ....6;
..... ...96, ..384, ..636, ..744, ..636, ..384, ...96;
.2976, 11904, 20256, 26304, 28536, 26304, 20256, 11904, .2976;
then the first term in each row is the sum of the previous row:
2976 = 96 + 384 + 636 + 744 + 636 + 384 + 96
the next term is 4 times the first:
11904 = 4*2976,
and the remaining terms in each row are obtained by the rule
illustrated by:
20256 = 2*11904 - 2976 - 6*96;
26304 = 2*20256 - 11904 - 6*384;
28536 = 2*26304 - 20256 - 6*636;
26304 = 2*28536 - 26304 - 6*744;
20256 = 2*26304 - 28536 - 6*636;
11904 = 2*20256 - 26304 - 6*384;
2976 = 2*11904 - 20256 - 6*96.
An alternate recurrence is illustrated by:
11904 = 2976 + 3*(96 + 384 + 636 + 744 + 636 + 384 + 96);
20256 = 11904 + 3*(384 + 636 + 744 + 636 + 384);
26304 = 20256 + 3*(636 + 744 + 636);
28536 = 26304 + 3*(744);
and then for k>n, T(n,k) = T(n,2n-k).
PROG
(PARI) T(n, k)=local(p=3); if(2*n<k || k<0, 0, if(n==0 && k==0, 1, if(k==0, sum(j=0, 2*n-2, T(n-1, j)), if(k==1, (p+1)*T(n, 0), if(k<=n, 2*T(n, k-1)-T(n, k-2)-2*p*T(n-1, k-2), T(n, 2*n-k))))))
(PARI) /* Alternate Recurrence: */ T(n, k)=local(p=3); if(2*n<k || k<0, 0, if(n==0 && k==0, 1, if(k==0, sum(j=0, 2*n-2, T(n-1, j)), if(k<=n, T(n, k-1)+p*sum(j=k-1, 2*n-1-k, T(n-1, j)), T(n, 2*n-k)))))
CROSSREFS
Cf. A126151 (column 0); diagonals: A126152, A126153; A126154; variants: A008301, A125053, A126155.
Sequence in context: A343599 A191714 A370356 * A374370 A364509 A349545
KEYWORD
nonn,tabl
AUTHOR
Paul D. Hanna, Dec 19 2006
STATUS
approved