

A276983


Semiprimes n such that n1 or n+1 is prime.


1



4, 6, 10, 14, 22, 38, 46, 58, 62, 74, 82, 106, 158, 166, 178, 194, 226, 262, 278, 314, 346, 358, 382, 398, 422, 458, 466, 478, 502, 542, 562, 586, 614, 662, 674, 718, 734, 758, 838, 862, 878, 886, 982, 998, 1018, 1094, 1154, 1186, 1202, 1214, 1238, 1282, 1306, 1318, 1322
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OFFSET

1,1


COMMENTS

Union of A077065 and A077068.


LINKS

Robert Israel, Table of n, a(n) for n = 1..10000


FORMULA

a(n) = 2*A120628(n).


EXAMPLE

a(3) = 10 = 2*5 is a product of 2 primes and 10+1 = 11 is prime.
a(4) = 14 = 2*7 is a product of 2 primes and 141 = 13 is prime.


MAPLE

select(t > isprime(t/2) and (isprime(t1) or isprime(t+1)), [seq(i, i=2..10000, 2)]); # Robert Israel, Sep 30 2016


MATHEMATICA

func[n_] := PrimeOmega[n] == 2 && (PrimeQ[n + 1]  PrimeQ[n  1])
Select[Range[1000], func[#] &]


PROG

(PARI) isok(n) = (bigomega(n)==2) && (isprime(n1)  isprime(n+1)); \\ Michel Marcus, Sep 24 2016
(PARI) lista(nn) = forprime(p=2, nn, if(isprime(2*p+1)  isprime(2*p1), print1(2*p, ", "))); \\ Altug Alkan, Sep 30 2016


CROSSREFS

Cf. A001358, A077065, A077068, A120628.
Sequence in context: A141247 A049632 A216732 * A061227 A274522 A000066
Adjacent sequences: A276980 A276981 A276982 * A276984 A276985 A276986


KEYWORD

nonn


AUTHOR

Gary E. Davis, Sep 24 2016


STATUS

approved



