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A276983 Semiprimes n such that n-1 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 (list; graph; refs; listen; history; text; internal format)
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 14-1 = 13 is prime.

MAPLE

select(t -> isprime(t/2) and (isprime(t-1) 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(n-1) || isprime(n+1)); \\ Michel Marcus, Sep 24 2016

(PARI) lista(nn) = forprime(p=2, nn, if(isprime(2*p+1) || isprime(2*p-1), 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

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Last modified September 17 12:40 EDT 2021. Contains 347477 sequences. (Running on oeis4.)