A067355 - OEIS

A067355

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.

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

1,1

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..10000

MATHEMATICA

f[n_] := f[n] = Prime[n] - n * DivisorSigma[0, n]; Select[Range[4, 20000], f[#+3] == f[#-3] &] (* Amiram Eldar, Apr 08 2024 *)

PROG

(PARI) f(n) = prime(n) - n * numdiv(n);

is(n) = n > 3 && f(n+3) == f(n-3); \\ Amiram Eldar, Apr 08 2024

CROSSREFS

Cf. A000005, A067292, A067293, A067335, A067356.

Sequence in context: A141282 A336181 A354590 * A138362 A191499 A072372

Adjacent sequences: A067352 A067353 A067354 * A067356 A067357 A067358

KEYWORD

easy,nonn

AUTHOR

Benoit Cloitre, Feb 24 2002

STATUS

approved