Second differences of Motzkin numbers (A001006).

Terms

a(0) =1a(1) =3a(2) =7a(3) =18a(4) =46a(5) =120a(6) =316a(7) =841a(8) =2257a(9) =6103a(10) =16611a(11) =45475a(12) =125139a(13) =345957a(14) =960417a(15) =2676291a(16) =7483299a(17) =20989833a(18) =59042805a(19) =166520124a(20) =470781528a(21) =1333970190a(22) =3787707322a(23) =10775741271a(24) =30711538351a(25) =87677551081a(26) =250704001213a(27) =717923179762