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

Author

Zak Seidov, Sep 07 2016

Keywords

• nonn

Comments

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

Examples

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

Links

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

Crossrefs

Cf. A175666.

Programs

Mathematica

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

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