A256388 Numbers n such that a single prime is the arithmetic mean of 2 semiprimes whose difference is 2*n.

1, 3, 9, 15, 27, 39, 57, 69, 99, 105, 135, 147, 177, 189, 195, 225, 237, 267, 279, 309, 345, 417, 429, 459, 519, 567, 597, 615, 639, 657, 807, 819, 825, 855, 879, 1017, 1029, 1047, 1059, 1089, 1149, 1227, 1275, 1287, 1299, 1317, 1425, 1449, 1479, 1485, 1605

Offset

1,2

Comments

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

Subsequence of A256389.

Links

Table of n, a(n) for n=1..51.

Formula

Conjecture: a(n) = A001359(n)-2. - Benedict W. J. Irwin, Apr 26 2016

Example

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.

Crossrefs

Cf. A124936, A256381.

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

Sequence in context: A089632 A247643 A287351 * A082897 A363523 A339886

Adjacent sequences: A256385 A256386 A256387 * A256389 A256390 A256391

Keyword

nonn

Author

Michel Marcus, Mar 27 2015

Status

approved