login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo

Please make a donation to keep the OEIS running. We are now in our 56th year. In the past year we added 10000 new sequences and reached almost 9000 citations (which often say "discovered thanks to the OEIS").
Other ways to donate

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A335984 Numbers n such that more than half the positive members of the sequence -k^2 + n*k - 1 are primes. 1

%I

%S 4,5,7,9,11,19,21,31,33,39,49,51,81,99,101,123,129,159,171,177,189,

%T 231,291,441,879,1011,2751

%N Numbers n such that more than half the positive members of the sequence -k^2 + n*k - 1 are primes.

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

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

%C There are no more terms below 200000. - _Pontus von Brömssen_, Jul 06 2020

%e 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.

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

%p select(filter, [$1..10000]);

%Y Cf. A059036.

%K nonn,more

%O 1,1

%A _Robert Israel_, Jul 03 2020

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified November 26 09:38 EST 2020. Contains 338639 sequences. (Running on oeis4.)