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A189119
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Sums k of three consecutive odd numbers, all of which are composite, such that k is also the smallest in a set of three consecutive odd numbers, all of which are composite.
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0
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621, 867, 891, 897, 1023, 1239, 1413, 1587, 1881, 2091, 2115, 2145, 2169, 2403, 2451, 2505, 2601, 2769, 2871, 2889, 3003, 3129, 3171, 3231, 3237, 3243, 3399, 3417, 3423, 3435, 3441, 3471, 3477, 3501, 3807, 3813, 3933, 3993, 4029
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OFFSET
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1,1
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LINKS
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EXAMPLE
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621 is a term: it is the smallest of three consecutive odd composite numbers (621 = 3^3*23, 623 = 7*89, 625 = 5^4) and is also the sum of three consecutive odd composite numbers (205 = 5*41, 207 = 3^2*23, 209 = 11*19, and 205 + 207 + 209 = 621).
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MATHEMATICA
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fQ[n_]:=!PrimeQ[n]&&!PrimeQ[n+2]&&!PrimeQ[n+4];
lst1=Select[Range[3, 9000, 2], fQ];
lst2=3*Select[Range[3, 3000, 2], fQ]+6;
Intersection[lst1, lst2]
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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