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A358816
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Numbers k such that d + k/d is prime for any unitary divisor d of k.
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1
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1, 2, 4, 6, 10, 12, 16, 18, 22, 28, 30, 36, 40, 42, 52, 58, 60, 70, 72, 78, 82, 88, 100, 102, 108, 112, 130, 148, 162, 172, 190, 192, 196, 198, 210, 228, 232, 240, 250, 256, 268, 270, 280, 310, 312, 316, 330, 352, 358, 372, 378, 382, 388, 396, 400, 408, 432, 442, 448
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OFFSET
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1,2
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COMMENTS
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A unitary divisor d of k is a number d such that d|k and gcd(d, k/d) = 1.
A080715 is the subsequence of the squarefree terms of this sequence.
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LINKS
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MATHEMATICA
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q[n_] := AllTrue[Select[Divisors[n], #^2 < n && CoprimeQ[#, n/#] &], PrimeQ[# + n/#] &]; Select[Prime[Range[90]] - 1, q]
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PROG
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(PARI) is(n) = fordiv(n, d, if(d < n^2 && gcd(d, n/d) == 1 && !isprime(d+n/d), return(0))); return(1);
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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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