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A128286 a[n]= is the n-th smallest product of 5 odd primes m=p1*p2*p3*p4*p5, such that (d+m/d)/2 are all primes for each d dividing m. 4
884037, 1137565, 2398377, 123156993, 681714273, 2347722213, 7283144845, 7794246057, 8953447917, 10287992785, 13749228493, 38108016453, 38901676405, 70918253385, 71809744693, 120418624965, 148282565865, 150721729873 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

a[6]>10^9

LINKS

Table of n, a(n) for n=1..18.

EXAMPLE

eg 884037 = 3*7*11*43*89 and (1+884037)/2, (3+7*11*43*89)/2,

(7+3.11.43.89)/2, (11+3.7.43.89)/2, (43+3.7.11.89)/2, (89+3.7.11.43)/2,

(3.7+11.43.89)/2, (3.11+7.43.89)/2, (3.43+7.11.89)/2,(3.89+7.11.43)/2,

(7.11+3.43.89)/2, (7.43+3.7.89)/2, (7.89+3.7.43)/2, (11.43+3.7.89)/2,

(11.89+3.7.43)/2, (43*89+3*7*11)/2 are all primes and 884037 is the smallest such integer, so a[1]=884037

CROSSREFS

Cf. A128281, A005383, A128283, A128284, A128285.

Sequence in context: A253982 A273036 A251409 * A250571 A092016 A269219

Adjacent sequences:  A128283 A128284 A128285 * A128287 A128288 A128289

KEYWORD

hard,nonn

AUTHOR

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

EXTENSIONS

a(6)-a(18) from Donovan Johnson, Oct 12 2008

STATUS

approved

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Last modified October 15 00:14 EDT 2019. Contains 328025 sequences. (Running on oeis4.)