A128277 a(n) is the n-th smallest integer m which is the product of 4 odd primes m=p1*p2*p3*p4 such that d+2*m/d are all primes for each d dividing 2*m.

93081, 449985, 1523705, 301921991, 899343761, 1581262341, 7290929465, 12102153569, 25404516309, 27482957831, 38661868781, 49656488021, 240305617889, 305000299185, 341656377581, 377737353491

Offset

1,1

Comments

1. a(6) > 2*10^9

2. (C. Pomerance) The prime k-tuple conjecture implies the sequence is infinite.

a(17) > 4*10^11. - Donovan Johnson, Sep 06 2010

Links

Table of n, a(n) for n=1..16.

Example

93081 = 3*19*23*71 and 2*93081+1, 2+3*19*23*71, 3+2*19*23*71, 19+2*3*23*71, 71+2*3*19*23, 2*3+19*23*71, 2*19+3*23*71, 2*23+3*19*23*71, 2*71+3*19*23, 3*19+2*23*71, 3*23+2*19*71, 3*71+2*19*23, 19*23+2*3*71, 19*71+2*3*23, 23*71+2*3*19 are all primes and 93081 is smallest such integer, so a(1)=93081.

Crossrefs

Cf. A128276.

Sequence in context: A225890 A183853 A331361 * A237682 A023945 A203784

Adjacent sequences: A128274 A128275 A128276 * A128278 A128279 A128280

Keyword

hard,more,nonn

Author

Kok Seng Chua (chuakokseng(AT)hotmail.com), Feb 23 2007

Extensions

Changed every occurrence of 93801 to 93081. - T. D. Noe, Aug 05 2010

Added missing term 899343761 and a(7)-a(16) from Donovan Johnson, Sep 06 2010

Status

approved