%I #7 Jun 15 2022 14:36:49
%S 12,21,39,48,57,75,93,111,129,147,183,192,201,219,237,291,309,327,363,
%T 381,417,453,471,489,507,543,579,597,633,669,687,723,768,813,831,849,
%U 867,921,939,993,1011,1029,1047,1083,1101,1119,1137,1191,1227,1263,1299,1317,1371,1389,1461,1497,1569,1587,1623,1641,1713
%N Numbers that are 3 * prime powers congruent to 1 (mod 3).
%C Numbers k of the form 9m+3 such that k/3 = p^k, with p a prime and k >= 1.
%F a(n) = 3 * A137827(n).
%t Select[Range[2000], Mod[#, 9] == 3 && PrimePowerQ[#/3] &] (* _Amiram Eldar_, Jun 15 2022 *)
%o (PARI)
%o A354983(n) = ((3==(n%9)) && isprimepower(n/3));
%o isA354984(n) = A354983(n);
%Y Intersection of A017197 and 3*A246655.
%Y Cf. A137827, A354983 (characteristic function).
%Y Row 3 of A354930 (conjectured).
%K nonn
%O 1,1
%A _Antti Karttunen_, Jun 15 2022