A276626 Semiprimes n such that (n-1)/3 is prime.

10, 22, 34, 58, 94, 142, 178, 202, 214, 382, 394, 454, 502, 538, 634, 718, 922, 934, 1042, 1138, 1294, 1318, 1402, 1438, 1642, 1714, 1762, 1822, 1858, 1894, 1942, 2182, 2218, 2362, 2434, 2518, 2578, 2722, 2734, 2902, 2974, 3118, 3274, 3694, 3778, 3958, 4198, 4282, 4414, 4534, 4594, 4678

Offset

1,1

Comments

All semiprimes in A175666 are terms: a(2)=10=A175666(2), a(3)=34=A175666(4),etc.

Links

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

Example

10=2*5 and (10-1)/3=3 prime, 22=2*11 and (22-1)/3=7 prime.

Mathematica

Reap[Do[If[PrimeQ[(a=1+3*Prime[k])/2], Sow[a]], {k, 1000}]][[2, 1]]

Prog

(PARI) isok(n) = (bigomega(n)==2) && (((n-1) % 3)==0) && isprime((n-1)/3); \\ Michel Marcus, Sep 07 2016
(PARI) is(n)=n%3==1 && isprime(n\3) && bigomega(n)==2 \\ Charles R Greathouse IV, Sep 07 2016

Crossrefs

Cf. A175666.

Sequence in context: A017641 A232540 A217573 * A211482 A177791 A028569

Adjacent sequences: A276623 A276624 A276625 * A276627 A276628 A276629

Keyword

nonn

Author

Zak Seidov, Sep 07 2016

Status

approved