A272903 - OEIS

A272903

Least nonnegative integer x such that n^2+nx-2n-x is prime.

2, 0, 1, 1, 1, 1, 5, 1, 1, 1, 1, 2, 1, 2, 1, 1, 5, 2, 1, 1, 1, 4, 5, 1, 17, 1, 3, 1, 13, 1, 1, 2, 3, 2, 1, 2, 5, 1, 1, 4, 1, 2, 5, 1, 1, 1, 13, 1, 11, 1, 3, 5, 1, 1, 1, 1, 5, 7, 1, 1, 11, 2, 3, 1, 1, 1, 7, 1, 3, 1, 11, 3, 5, 2, 3, 1, 17, 3, 7, 4, 3, 7, 1, 3, 1, 1, 3, 2, 1, 3, 11, 2, 1, 1, 7, 1, 17, 5, 9

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OFFSET

2,1

COMMENTS

The offset is 2 because n^2+nx-2n-x = -1 for n = 1 and all x.

a(n) seems to be exclusively prime or a product of two previous terms, and less than n excluding n = 2. x is most frequently equal to 1.

LINKS

Cody M. Haderlie, Table of n, a(n) for n = 2..10000

MATHEMATICA

Table[Min[DeleteCases[Table[If[PrimeQ[n^2+n*x-2n-x], x], {x, 0, n}], Null]], {n, 2, 100}] (*Assuming that x<n.*)

lni[n_]:=Module[{x=0}, While[!PrimeQ[n^2+n*x-2n-x], x++]; x]; Array[lni, 100, 2] (* Harvey P. Dale, May 12 2019 *)

CROSSREFS