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.

3, 15, 105, 93081

Offset: 1

Author

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

Keywords

• hard
• more
• nonn

Comments

1. a(5) > 2*10^9 2. (C. Pomerance) The prime k-tuple conjecture implies a(n) exists for all n

Examples

			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
		

Extensions

Typo in a(4) corrected by T. D. Noe, Aug 04 2010