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A128283 a[n]= is the n-th smallest product of 2 odd primes m=p1*p2, such that (d+m/d)/2 are all primes for each d dividing m. 4
21, 33, 57, 85, 93, 133, 145, 177, 205, 213, 217, 253, 393, 445, 553, 565, 633, 697, 793, 817, 865, 913, 933, 973, 1137, 1285, 1345, 1417, 1437, 1465, 1477, 1513, 1537, 1717, 1765, 1837, 1857, 1893, 2101, 2173, 2245, 2305, 2517, 2577, 2581, 2605, 2641, 2653 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..48.

EXAMPLE

85=5.17, (5.17+1)/2=43, (5+17)/2=11 are both primes and 85 is the 4th such integer, so a[4]=85

CROSSREFS

Cf. A128281, A005383, A128284, A128285, A128286.

Sequence in context: A191683 A032603 A233562 * A280878 A033901 A033656

Adjacent sequences:  A128280 A128281 A128282 * A128284 A128285 A128286

KEYWORD

nonn

AUTHOR

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

STATUS

approved

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Last modified September 20 12:43 EDT 2019. Contains 327238 sequences. (Running on oeis4.)