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Numbers n such that a single prime is the arithmetic mean of 2 semiprimes whose difference is 2*n.
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%I #12 Apr 26 2016 09:03:16

%S 1,3,9,15,27,39,57,69,99,105,135,147,177,189,195,225,237,267,279,309,

%T 345,417,429,459,519,567,597,615,639,657,807,819,825,855,879,1017,

%U 1029,1047,1059,1089,1149,1227,1275,1287,1299,1317,1425,1449,1479,1485,1605

%N Numbers n such that a single prime is the arithmetic mean of 2 semiprimes whose difference is 2*n.

%C That is, there is a single prime p, such that p+n and p-n are both semiprime.

%C Subsequence of A256389.

%F Conjecture: a(n) = A001359(n)-2. - _Benedict W. J. Irwin_, Apr 26 2016

%e A256381 is the list of numbers n such that n-3 and n+3 are semiprimes, and it contains a single prime, hence 3 is in the sequence.

%Y Cf. A124936, A256381.

%Y Cf. A256387 (no prime), A256389 (one or more primes).

%K nonn

%O 1,2

%A _Michel Marcus_, Mar 27 2015