OFFSET
0,3
COMMENTS
Sequence of row lengths = A001651.
LINKS
J. Stauduhar, Table of n, a(n) for n = 0..719
FORMULA
T(n,k) = A222656(3n,k).
EXAMPLE
The irregular triangle T(n, k) begins:
3n\k 0 1 2 3 4 5 6 7 8 9
0: 1
3: 1 2
6: 3 4 3 1
9: 6 9 8 5 2
12: 12 20 19 14 8 3 1
15: 19 41 42 34 21 12 5 2
18: 37 72 88 74 53 31 18 8 3 1
MAPLE
b:= proc(n, i) option remember; expand(`if`(n=0 or i=1, 1,
add(b(n-i*j, i-1)*`if`(isprime(i), x^j, 1), j=0..n/i)))
end:
T:= n-> (p-> seq(coeff(p, x, i), i=0..degree(p)))(b(3*n$2)):
seq(T(n), n=0..12); # Alois P. Heinz, Mar 03 2018
MATHEMATICA
b[n_, i_] := b[n, i] = Expand[If[n == 0 || i == 1, 1,
Sum[b[n - i*j, i - 1]*If[PrimeQ[i], x^j, 1], {j, 0, n/i}]]];
T[n_] := CoefficientList[b[3n, 3n], x];
T /@ Range[0, 12] // Flatten (* Jean-François Alcover, Mar 08 2021, after Alois P. Heinz *)
CROSSREFS
KEYWORD
nonn,tabf
AUTHOR
J. Stauduhar, Feb 17 2018
STATUS
approved