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A128281
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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.
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4
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OFFSET
| 1,1
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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.
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CROSSREFS
| Cf. A128276, A128282, A128283, A128284, A128285, A128286.
Sequence in context: A074597 A076207 A134057 * A034268 A140451 A054147
Adjacent sequences: A128278 A128279 A128280 * A128282 A128283 A128284
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KEYWORD
| hard,more,nonn
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AUTHOR
| Kok Seng Chua (chuakokseng(AT)hotmail.com), Mar 05 2007
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