a(1) = 1; a(n) = nextprime(2.5*a(n-1)) for n > 1.

Terms

a(0) =1a(1) =3a(2) =11a(3) =29a(4) =73a(5) =191a(6) =479a(7) =1201a(8) =3011a(9) =7529a(10) =18839a(11) =47111a(12) =117779a(13) =294461a(14) =736159a(15) =1840429a(16) =4601099a(17) =11502779a(18) =28756957a(19) =71892397a(20) =179730997a(21) =449327503a(22) =1123318769a(23) =2808296923a(24) =7020742321a(25) =17551855831a(26) =43879639613a(27) =109699099033