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%I #29 Sep 05 2023 05:50:47
%S 15,21,33,39,51,57,69,87,93,111,123,129,141,159,177,183,201,213,219,
%T 237,249,267,291,303,309,321,327,339,381,393,411,417,447,453,471,489,
%U 501,519,537,543,573,579,591,597,633,669,681,687,699,717,723,753,771,789
%N Semiprimes equal to the sum of three primes in arithmetic progression.
%F Conjecture: a(n) = 3*A000040(n+2). - _Zak Seidov_, Jun 28 2015
%F Every member of the sequence is 3 times a prime; it is believed that every prime >= 5 arises in this way. This is related to Goldbach's conjecture: see comments to A078611. - _Robert Israel_ and _Michel Marcus_, Jun 28 2015
%e a(1) = 15 because 15 = 3 + 5 + 7;
%e a(2) = 21 because 21 = 3 + 7 + 11.
%o (Magma) [3*NthPrime(n+2): n in [1..60]]; // _Vincenzo Librandi_, Jun 28 2015, assuming the conjecture holds
%Y Cf. A000040, A001358, A078611.
%K easy,nonn
%O 1,1
%A _Giovanni Teofilatto_, Mar 30 2007
%E Corrected (57 = 7+19+31), 87 = 5+29+53, etc. inserted) by _R. J. Mathar_, Apr 22 2010
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