Pentagonal numbers with even index.

Terms

a(0) =0a(1) =5a(2) =22a(3) =51a(4) =92a(5) =145a(6) =210a(7) =287a(8) =376a(9) =477a(10) =590a(11) =715a(12) =852a(13) =1001a(14) =1162a(15) =1335a(16) =1520a(17) =1717a(18) =1926a(19) =2147a(20) =2380a(21) =2625a(22) =2882a(23) =3151a(24) =3432a(25) =3725a(26) =4030a(27) =4347a(28) =4676a(29) =5017