A075862 Numbers m such that the least k such that (m-k) divides (m+k) is prime.

4, 5, 6, 7, 9, 10, 13, 14, 15, 19, 21, 22, 26, 31, 33, 34, 38, 39, 43, 46, 51, 57, 58, 61, 62, 69, 73, 74, 82, 86, 87, 93, 94, 103, 106, 109, 111, 118, 122, 123, 129, 134, 139, 141, 142, 146, 151, 158, 159, 166, 177, 178, 181, 183, 193, 194, 199, 201, 202, 206, 213

Offset

1,1

Links

Table of n, a(n) for n=1..61.

Formula

a(n) seems to be asymptotic to n*log(n) and a(n)<prime(n) for n>3.

Mathematica

plkQ[n_]:=Module[{k=2}, While[!Divisible[n+k, n-k], k++]; PrimeQ[k]]; Select[ Range[ 4, 250], plkQ] (* Harvey P. Dale, Dec 29 2018 *)

Prog

(PARI) f(m) = if (m>1, my(k=1); while ((m+k) % (m-k), k++); k); \\ A075861
isok(m) = isprime(f(m)); \\ Michel Marcus, Feb 19 2021

Crossrefs

Cf. A075861.

Sequence in context: A066485 A079445 A120173 * A088685 A022299 A099049

Adjacent sequences: A075859 A075860 A075861 * A075863 A075864 A075865

Keyword

nonn

Author

Benoit Cloitre, Oct 15 2002

Status

approved