Numbers k such that k and k-1 both have 6 divisors.

Terms

a(0) =45a(1) =76a(2) =99a(3) =117a(4) =148a(5) =172a(6) =243a(7) =244a(8) =245a(9) =333a(10) =388a(11) =508a(12) =549a(13) =604a(14) =605a(15) =725a(16) =845a(17) =909a(18) =932a(19) =964a(20) =1076a(21) =1084a(22) =1252a(23) =1325a(24) =1413a(25) =1468a(26) =1557a(27) =1588a(28) =1676a(29) =1773