Concatenation of 'nextprime(a(n)) and a(n)' and 'a(n) and nextprime(a(n))' are both prime.

Terms

a(0) =27a(1) =51a(2) =63a(3) =123a(4) =199a(5) =217a(6) =219a(7) =233a(8) =257a(9) =341a(10) =353a(11) =357a(12) =417a(13) =423a(14) =429a(15) =473a(16) =501a(17) =519a(18) =523a(19) =551a(20) =579a(21) =597a(22) =609a(23) =653a(24) =657a(25) =667a(26) =669a(27) =687a(28) =703a(29) =717