A127329 Semiprimes equal to the sum of three primes in arithmetic progression.

15, 21, 33, 39, 51, 57, 69, 87, 93, 111, 123, 129, 141, 159, 177, 183, 201, 213, 219, 237, 249, 267, 291, 303, 309, 321, 327, 339, 381, 393, 411, 417, 447, 453, 471, 489, 501, 519, 537, 543, 573, 579, 591, 597, 633, 669, 681, 687, 699, 717, 723, 753, 771, 789

Offset

1,1

Links

Table of n, a(n) for n=1..54.

Formula

Conjecture: a(n) = 3*A000040(n+2). - Zak Seidov, Jun 28 2015

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

Example

a(1) = 15 because 15 = 3 + 5 + 7;
a(2) = 21 because 21 = 3 + 7 + 11.

Prog

(Magma) [3*NthPrime(n+2): n in [1..60]]; // Vincenzo Librandi, Jun 28 2015, assuming the conjecture holds

Crossrefs

Cf. A000040, A001358, A078611.

Sequence in context: A300117 A214044 A177516 * A043326 A179996 A079814

Adjacent sequences: A127326 A127327 A127328 * A127330 A127331 A127332

Keyword

easy,nonn

Author

Giovanni Teofilatto, Mar 30 2007

Extensions

Corrected (57 = 7+19+31), 87 = 5+29+53, etc. inserted) by R. J. Mathar, Apr 22 2010

Status

approved