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Numbers that are 3 * prime powers congruent to 1 (mod 3).
4

%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