Odd integers k>=3 such that k*(k-1)/2 divides 2^((k-1)/2)+1.

Terms

a(0) =3a(1) =19a(2) =163a(3) =1459a(4) =370387a(5) =6381667a(6) =30001267a(7) =40417219a(8) =42384547a(9) =42633379a(10) =86093443a(11) =190008019a(12) =268435459a(13) =634471219a(14) =1630068787a(15) =2415919123a(16) =3103616899a(17) =4677743683a(18) =7734924739a(19) =7920392707a(20) =8114552947a(21) =10323768979a(22) =13086951139a(23) =13984274323a(24) =18839387107a(25) =19764019603a(26) =36164859427