Numbers k such that the period of the continued fraction for sqrt(k) contains exactly four 1's.

Terms

a(0) =13a(1) =21a(2) =31a(3) =57a(4) =61a(5) =67a(6) =73a(7) =74a(8) =92a(9) =106a(10) =108a(11) =109a(12) =111a(13) =112a(14) =116a(15) =129a(16) =137a(17) =158a(18) =161a(19) =162a(20) =183a(21) =185a(22) =193a(23) =204a(24) =207a(25) =236a(26) =237a(27) =243a(28) =246a(29) =251