

A128281


a[n] = is the least product of n odd primes m=p1*p2*...*pn, such that (d+m/d)/2 are all primes for each d dividing m.


4




OFFSET

1,1


LINKS

Table of n, a(n) for n=1..5.


EXAMPLE

105=3.5.7, (3.5.7+1)/2=53, (3+5.7)/2=19, (5+3.7)/2=13, (7+3.5)/2=11 are all primes and 105 is the least such number which is the product of 3 primes, so a[3]=3.


CROSSREFS

Cf. A128276, A128282, A128283, A128284, A128285, A128286.
Sequence in context: A306093 A076207 A134057 * A034268 A140451 A054147
Adjacent sequences: A128278 A128279 A128280 * A128282 A128283 A128284


KEYWORD

hard,more,nonn


AUTHOR

Kok Seng Chua (chuakokseng(AT)hotmail.com), Mar 05 2007


STATUS

approved



