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A335984 Numbers n such that more than half the positive members of the sequence -k^2 + n*k - 1 are primes. 1
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Numbers n such that more than half the terms in row n of the triangular array A059036 are prime.

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

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

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 members 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.

Sequence in context: A283554 A035243 A035255 * A286050 A047493 A285307

Adjacent sequences:  A335981 A335982 A335983 * A335985 A335986 A335988

KEYWORD

nonn,more

AUTHOR

Robert Israel, Jul 03 2020

STATUS

approved

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Last modified October 27 06:09 EDT 2020. Contains 338035 sequences. (Running on oeis4.)