a(n) = number of integer strings s(0),...,s(n) counted by array T in A026374 that have s(n)=4; also a(n) = T(2n,n-2).

A026377

a(n) = number of integer strings s(0),...,s(n) counted by array T in A026374 that have s(n)=4; also a(n) = T(2n,n-2).

Terms

    a(0) =1a(1) =9a(2) =58a(3) =330a(4) =1770a(5) =9198a(6) =46928a(7) =236736a(8) =1185645a(9) =5909805a(10) =29362806a(11) =145570230a(12) =720606705a(13) =3563543025a(14) =17610412600a(15) =86989143480a(16) =429579843435

External references