Indices of pentagonal numbers > 0 which are not the difference of 2 other pentagonal numbers > 0.

Terms

a(0) =1a(1) =2a(2) =3a(3) =6a(4) =8a(5) =9a(6) =11a(7) =15a(8) =18a(9) =24a(10) =27a(11) =54a(12) =81a(13) =96a(14) =128a(15) =135a(16) =162a(17) =216a(18) =243a(19) =288a(20) =303a(21) =384a(22) =423a(23) =459a(24) =486a(25) =519a(26) =591a(27) =639a(28) =648a(29) =683