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A225916
Product of distinct primes p*q such that both 2p + q and p + 2q are prime numbers.
2
15, 21, 35, 39, 51, 65, 95, 119, 141, 155, 159, 161, 185, 201, 219, 221, 291, 305, 329, 341, 365, 371, 395, 471, 485, 501, 515, 519, 579, 581, 611, 669, 681, 695, 779, 791, 815, 831, 851, 905, 921, 959, 989, 1059, 1079, 1121, 1139, 1145, 1149, 1199, 1205, 1241
OFFSET
1,1
EXAMPLE
15=3*5, both 2*3+5=11 and 3+2*5=13 are prime number, so 15 is a term of this sequence.
MATHEMATICA
NextA046388[n_] := Block[{p1 = Prime[Range[2, PrimePi[Max[3, NextPrime[Ceiling@Sqrt[n + 1] - 1]]]]], p2}, p2 = Table[Max[NextPrime[p1[[i]]], NextPrime[Ceiling[(n + 1)/p1[[i]]] - 1]], {i, Length[p1]}]; Min[p1*p2]]; seed=1; Table[While[seed = NextA046388[seed]; fct = FactorInteger[seed]; p1 = fct[[1, 1]]; p2 = fct[[2, 1]]; c1 = 2*p1 + p2; c2 = p1 + 2*p2; ! ((PrimeQ[c1]) && (PrimeQ[c2]))]; seed, {i, 1, 52}]
nn = 1241; pq = Select[Range[nn], PrimeOmega[#] == 2 &]; p = Table[FactorInteger[r][[1, 1]], {r, pq}]; q = pq/p; t = {}; Do[If[PrimeQ[2 p[[i]] + q[[i]]] && PrimeQ[p[[i]] + 2 q[[i]]], AppendTo[t, pq[[i]]]], {i, Length[pq]}]; t (* T. D. Noe, May 21 2013 *)
CROSSREFS
Cf. A046388.
Sequence in context: A346812 A296244 A309005 * A128279 A099611 A081934
KEYWORD
nonn
AUTHOR
Lei Zhou, May 20 2013
STATUS
approved