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A303379
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Primes p such that p == 1 (mod 6), p-2 is composite, and for all r in the range 5 <= r < p - 2, p-2 is not congruent to r (mod r*(r + 1)/2).
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1
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163, 223, 439, 499, 613, 691, 733, 769, 919, 1009, 1039, 1123, 1249, 1423, 1459, 1543, 1579, 1693, 1741, 1753, 1759, 2179, 2203, 2251, 2281, 2293, 2371, 2503, 2539, 2671, 2683, 2749, 2833, 2953, 3019, 3163, 3319, 3343, 3499, 3739, 3793, 3943, 4099, 4363, 4513, 4603
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OFFSET
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1,1
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COMMENTS
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The term r*(r + 1)/2 is the triangular number T(r).
If p - 2 is composite, a(n) is not the greater member (A006512) p >= 7 of a twin prime, although such p always meet the remaining conditions.
The set {a(n)}+{A006512}/{5} is one of four disjunct classes of primes p >= 7 dependent on all cases of the two conditions p == [1 | 5] (mod 6) and if in the range 5 <= r < p - 2 [at least one | not any] r exists with p - 2 == r (mod r*(r + 1)/2).
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LINKS
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MATHEMATICA
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lst = {}; Do[p = Prime[n]; f = False;
If[1 == Mod[p, 6], f = True;
Do[If[r == Mod[p - 2, 1/2 r (1 + r)], f = False], {r, 5, p - 3}]];
If[f && ! PrimeQ[p - 2], lst = AppendTo[lst, p]], {n, 1, 500}]; lst
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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