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A127166
a(n) = the minimum prime S possible, if S = product of b(k)'s + product of c(k)'s, where the distinct positive integers <= n are partitioned into the two sets {b(k)} and {c(k)}. a(n) = 0 if no prime S exists for that n.
3
2, 2, 3, 5, 11, 23, 149, 179, 1187, 0, 0, 3628811, 43545611, 43545743, 7925299211, 9144576143, 1609445376013, 32335220736011, 44771844096143, 582033973248209, 52672757806189, 18804174520322717, 267682954936324199
OFFSET
0,1
COMMENTS
a(0)=a(1)=2 because the product over the empty set is defined here as 1. For S to be a prime, the positive integers <= n, except 1 and the primes > n/2, must all be together in either {b(k)} or {c(k)}. If p is a prime where n/2 < p <= n, then it is possible that p is in either product of the S sum, as can 1. Terms calculated by W. Edwin Clark.
LINKS
EXAMPLE
For n = 6 we have the only prime S (and so the minimum prime S) with S = 1*2*3*4*6 + 5 = 149.
MATHEMATICA
f[n_] := Block[{d = Divisors[Times @@ Select[Range[n], PrimeQ[ # ] && 2# > n &]]}, Select[Union[d + n!/d], PrimeQ]]; If[ # == {}, 0, First[ # ]] & /@ Array[f, 30, 0] (* Ray Chandler, Feb 14 2007 *)
CROSSREFS
Sequence in context: A030427 A049907 A078445 * A103596 A005426 A014644
KEYWORD
nonn
AUTHOR
Leroy Quet, Jan 06 2007
EXTENSIONS
a(21)-a(35) from Ray Chandler, Feb 14 2007
STATUS
approved