a(n) = spt(7n+5)/7 where spt(n) = A092269(n).

Terms

a(0) =2a(1) =34a(2) =260a(3) =1498a(4) =6956a(5) =28024a(6) =100953a(7) =333680a(8) =1026540a(9) =2976024a(10) =8197962a(11) =21608760a(12) =54788100a(13) =134217717a(14) =318816426a(15) =736549424a(16) =1659169712a(17) =3652248590a(18) =7870890952a(19) =16633964444a(20) =34522173765a(21) =70450341042a(22) =141526909340a(23) =280158178412