A184778 - OEIS

%I #20 Jul 29 2022 09:56:31

%S 1,4,5,7,11,14,18,21,32,41,46,48,49,56,62,79,83,86,90,93,97,114,120,

%T 123,127,130,134,137,144,165,169,172,178,181,185,188,213,220,222,223,

%U 237,243,246,250,253,257,260,267,288,302,308,311,325,329,343,346,352,360,366,369,376

%N Numbers k such that 2k + floor(k*sqrt(2)) is prime.

%H G. C. Greubel, <a href="/A184778/b184778.txt">Table of n, a(n) for n = 1..10000</a>

%e See A184774.

%t r=2^(1/2); s=r/(r-1);

%t a[n_]:=Floor [n*r];  (* A001951 *)

%t b[n_]:=Floor [n*s];  (* A001952 *)

%t Table[a[n],{n,1,120}]

%t t1={}; Do[If[PrimeQ[a[n]], AppendTo[t1,a[n]]], {n,1,600}]; t1

%t t2={}; Do[If[PrimeQ[a[n]], AppendTo[t2,n]], {n,1,600}]; t2

%t t3={}; Do[If[MemberQ[t1, Prime[n]], AppendTo[t3,n]],{n,1,300}]; t3

%t t4={}; Do[If[PrimeQ[b[n]], AppendTo[t4,b[n]]],{n,1,600}]; t4

%t t5={}; Do[If[PrimeQ[b[n]], AppendTo[t5,n]],{n,1,600}]; t5

%t t6={}; Do[If[MemberQ[t4, Prime[n]], AppendTo[t6,n]],{n,1,300}]; t6

%t (* the lists t1,t2,t3,t4,t5,t6 match the sequences

%t A184774, A184775, A184776 ,A184777, A184778, A184779 *)

%o (PARI) is(n)=isprime(sqrtint(2*n^2)+2*n) \\ _Charles R Greathouse IV_, May 22 2017

%o (Python)

%o from itertools import count, islice

%o from math import isqrt

%o from sympy import isprime

%o def A184778_gen(): # generator of terms

%o     return filter(lambda k:isprime((k<<1)+isqrt(k**2<<1)), count(1))

%o A184778_list = list(islice(A184778_gen(),25)) # _Chai Wah Wu_, Jul 28 2022

%Y Cf. A184774, A184777, A184779.

%K nonn

%O 1,2

%A _Clark Kimberling_, Jan 21 2011