[seqfan] Convolve tribonacci with trinomials = A099464?

[David Scambler]

Apparently,

Sum {k=0..2n} ( tribonacci(k) * trinomial(n,k) ) = tribonacci(3n) = A099464.
Already known? Obvious?

Note that A074581 also claims to be tribonacci(3n) but I think it is actually tribonacci(3n+1).

A similar formula apparently applies,
Sum {k=0..2n} ( tribonacci(k+1) * trinomial(n,k) ) = tribonacci(3n+1) = A074581.

dave