Values of k such that k^2 + 9 is a triangular number (A000217).

Terms

a(0) =1a(1) =6a(2) =12a(3) =37a(4) =71a(5) =216a(6) =414a(7) =1259a(8) =2413a(9) =7338a(10) =14064a(11) =42769a(12) =81971a(13) =249276a(14) =477762a(15) =1452887a(16) =2784601a(17) =8468046a(18) =16229844a(19) =49355389a(20) =94594463a(21) =287664288a(22) =551336934a(23) =1676630339a(24) =3213427141a(25) =9772117746a(26) =18729225912a(27) =56956076137a(28) =109161928331a(29) =331964339076