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A067335
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Numbers k such that prime(k+1)-(k+1)*tau(k+1) = prime(k-1)-(k-1)*tau(k-1) where tau(k) = A000005(k) is the number of divisors of k.
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5
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202, 216, 471, 583, 816, 850, 894, 905, 922, 1277, 1335, 1386, 1594, 1712, 1774, 1942, 1958, 2554, 2760, 2777, 2840, 2876, 2934, 2944, 3132, 3438, 3566, 3694, 3900, 3980, 4013, 4188, 4342, 4352, 4526, 4594, 4627, 4686, 4808, 5268, 5730, 6032, 6326
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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[2, 6500], f[#+1] == f[#-1] &] (* 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 > 1 && f(n+1) == f(n-1); \\ 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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