At these values of k, the 1st, 2nd, 3rd and 4th cyclotomic polynomials all give prime numbers.

Terms

a(0) =6a(1) =150a(2) =2730a(3) =9000a(4) =9240a(5) =35280a(6) =41760a(7) =43050a(8) =53280a(9) =65520a(10) =76650a(11) =96180a(12) =111030a(13) =148200a(14) =197370a(15) =207480a(16) =213360a(17) =226380a(18) =254280a(19) =264600a(20) =309480a(21) =332160a(22) =342450a(23) =352740a(24) =375450a(25) =381990a(26) =440550a(27) =458790a(28) =501030a(29) =527070