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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

Table of n, a(n) for n=1..4.

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: A269455 A088109 A231634 * A295124 A107878 A218688

Adjacent sequences:  A128273 A128274 A128275 * A128277 A128278 A128279

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

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Last modified February 19 13:02 EST 2019. Contains 320310 sequences. (Running on oeis4.)