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!)
A128276 a(n) is the least product of n odd primes m=p1*p2*...*pn, such that for all divisor d|2*m, d+2*m/d is prime. 5
3, 15, 105, 93081 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
1. a(5) > 2*10^9 2. (C. Pomerance) The prime k-tuple conjecture implies a(n) exists for all n
LINKS
EXAMPLE
105=3*5*7 and 2*3*5*7+1, 3*5*7+2, 2*5*7+3, 2*3*7+5, 2*3*5+7, 2*3+5*7, 2*5+3*7, 2*7+3*5 are all primes and 105 is the smallest such integer which is the product of 3 odd primes, so a(3)=105
CROSSREFS
Sequence in context: A088109 A231634 A353587 * A295124 A107878 A218688
KEYWORD
hard,more,nonn
AUTHOR
Kok Seng Chua (chuakokseng(AT)hotmail.com), Feb 23 2007
EXTENSIONS
Typo in a(4) corrected by T. D. Noe, Aug 04 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 March 29 05:48 EDT 2024. Contains 371265 sequences. (Running on oeis4.)