A335984 Numbers m such that more than half the distinct positive terms of the sequence -k^2 + m*k - 1 are primes.

4, 5, 7, 9, 11, 19, 21, 31, 33, 39, 49, 51, 81, 99, 101, 123, 129, 159, 171, 177, 189, 231, 291, 441, 879, 1011, 2751

Offset

1,1

Comments

Numbers m such that more than half the distinct terms in row m-2 of the triangular array A059036 are prime.

All positive terms of the sequence are prime for m = 1, 2, 4, 5, 9 and 21.

There are no more terms below 200000. - Pontus von Brömssen, Jul 06 2020

Numbers m such that A109909(m) > m/4. - Pontus von Brömssen, May 09 2021

Links

Table of n, a(n) for n=1..27.

Example

7 is in the sequence because with g(k) = -k^2+7*k-1, the positive terms of the sequence g(k) are 5=g(1), 9=g(2) and 11=g(3), and two out of the three (5 and 9) are prime.

Maple

filter:= n -> nops(select(isprime, [seq(n*x-x^2-1, x=1..n/2)])) > 1/2*floor(n/2):
select(filter, [$1..10000]);

Crossrefs

Cf. A059036, A109909.

Sequence in context: A035243 A035255 A341787 * A286050 A047493 A285307

Adjacent sequences: A335981 A335982 A335983 * A335985 A335986 A335987

Keyword

nonn,more

Author

Robert Israel, Jul 03 2020

Status

approved