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A127329 Semiprimes equal to the sum of three primes in arithmetic progression. 1
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 (list; graph; refs; listen; history; text; internal format)
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

CROSSREFS

Cf. A000040, A001358, A078611.

Sequence in context: A300117 A214044 A177516 * A099610 A043326 A179996

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

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Last modified September 19 20:55 EDT 2020. Contains 337182 sequences. (Running on oeis4.)