login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
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. 3
93081, 449985, 1523705, 301921991, 899343761, 1581262341, 7290929465, 12102153569, 25404516309, 27482957831, 38661868781, 49656488021, 240305617889, 305000299185, 341656377581, 377737353491 (list; graph; refs; listen; history; text; internal format)
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
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
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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified July 18 00:08 EDT 2024. Contains 374377 sequences. (Running on oeis4.)