0,2

a(n)=3a(n-1)-3a(n-3); a(n)=sum{k=0..floor(n/2), comb(n-2k, k)3^(n-2k) }.

Sequence in context: A006684 A018788 A098690 this_sequence A123888 A097134 A123892

Adjacent sequences: A090397 A090398 A090399 this_sequence A090401 A090402 A090403

easy,nonn

Paul Barry (pbarry(AT)wit.ie), Nov 28 2003