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A067355
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Numbers k such that prime(k+3)-(k+3)*tau(k+3) = prime(k-3)-(k-3)*tau(k-3) where tau(k) = A000005(k) is the number of divisors of k.
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5
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11, 47, 335, 373, 571, 1242, 1307, 1663, 3013, 3225, 3552, 4074, 4379, 4459, 4939, 5353, 5760, 5915, 6569, 7099, 7524, 7752, 8286, 8934, 9531, 10069, 10405, 10724, 10878, 11850, 13152, 13853, 14742, 15317, 15381, 15804, 17664, 17890, 18054
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OFFSET
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1,1
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LINKS
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MATHEMATICA
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f[n_] := f[n] = Prime[n] - n * DivisorSigma[0, n]; Select[Range[4, 20000], f[#+3] == f[#-3] &] (* Amiram Eldar, Apr 08 2024 *)
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PROG
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(PARI) f(n) = prime(n) - n * numdiv(n);
is(n) = n > 3 && f(n+3) == f(n-3); \\ Amiram Eldar, Apr 08 2024
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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STATUS
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approved
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