The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation. Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A082612 Numbers n such that ((n-1)^2+1)/2 and n^2+1 and ((n+1)^2+1)/2 are prime if n is even or (n-1)^2+1 and (n^2+1)/2 and (n+1)^2+1 are prime if n is odd. 5

%I

%S 3,4,5,10,15,25,170,205,570,715,780,950,1095,1315,1420,1615,2055,2380,

%T 2405,2730,2925,3755,3850,4120,4300,4615,4795,5015,5055,5475,5850,

%U 6360,6460,6785,6800,6970,7100,7240,7855,8115,8175,8720,9425,9475,9630,10150

%N Numbers n such that ((n-1)^2+1)/2 and n^2+1 and ((n+1)^2+1)/2 are prime if n is even or (n-1)^2+1 and (n^2+1)/2 and (n+1)^2+1 are prime if n is odd.

%C I believe this is an infinite sequence, though a proof seems to be still far off. 155th term is 62910. There are probably infinitely many consecutive n^2+1 or (n^2+1)/2 primes. That is, n^2+1 and (n+2)^2+1 or (n^2+1)/2 and ((n+2)^2+1)/2 are both prime infinitely often.

%H Harvey P. Dale, <a href="/A082612/b082612.txt">Table of n, a(n) for n = 1..1000</a>

%e a(4)=10 (9^2+1)/2=41 and 10^2+1=101 and (11^2+1)/2=61 are prime.

%t neoQ[n_]:=If[EvenQ[n],AllTrue[{((n-1)^2+1)/2,n^2+1,((n+1)^2+1)/2}, PrimeQ], AllTrue[{(n-1)^2+1, (n^2+1)/2,(n+1)^2+1},PrimeQ]]; Select[Range[ 6400], neoQ] (* The program uses the AllTrue function from Mathematica version 10 *) (* _Harvey P. Dale_, Mar 19 2018 *)

%K nonn

%O 1,1

%A _Robin Garcia_, Sep 23 2004

%E More terms from _Harvey P. Dale_, Mar 19 2018

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.

Last modified October 25 23:28 EDT 2021. Contains 348256 sequences. (Running on oeis4.)