login
a(n) is the constant term in expansion of Product_{k=1..n} (x^prime(k) + 1 + 1/x^prime(k))^2.
0

%I #5 Jan 22 2024 10:41:46

%S 1,3,9,45,249,1373,9177,62257,453179,3320531,24087877,183643865,

%T 1394580343,10794949627,85730722969,686171829489,5487361175591,

%U 43981108061647,358362244544957,2922625435214613,24006575088945973,199229783030494775,1653790732247194785

%N a(n) is the constant term in expansion of Product_{k=1..n} (x^prime(k) + 1 + 1/x^prime(k))^2.

%t Table[Coefficient[Product[(x^Prime[k] + 1 + 1/x^Prime[k])^2, {k, 1, n}], x, 0], {n, 0, 22}]

%Y Cf. A047653, A156181, A350880, A350881.

%K nonn

%O 0,2

%A _Ilya Gutkovskiy_, Jan 22 2024