(prime(n))^3-(nonprime(n))^3 .

Terms

a(0) =8a(1) =26a(2) =61a(3) =127a(4) =819a(5) =1468a(6) =3913a(7) =5131a(8) =9423a(9) =21014a(10) =25695a(11) =44821a(12) =60921a(13) =70246a(14) =93175a(15) =135053a(16) =189754a(17) =209405a(18) =281080a(19) =335959a(20) =362017a(21) =460271a(22) =535850a(23) =665665a(24) =869798a(25) =983645a(26) =1037855a(27) =1165724a(28) =1231029a(29) =1368809