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

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A217279 Numbers of the form n^2 + 1 without prime divisors of the form a^2 + 1. 1
1157, 1937, 2117, 2501, 3601, 4901, 5777, 7397, 9217, 10001, 10817, 12997, 18497, 20737, 26897, 34597, 36101, 37637, 38417, 45797, 48401, 51077, 59537, 60517, 64517, 70757, 75077, 81797, 86437, 87617, 92417, 99857, 102401, 104977, 108901, 111557, 119717 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The corresponding n are in A217276.

a(n) == 1, 17, 37, 57, 77, 97 mod 100.

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..10000

EXAMPLE

1157 is in the sequence because 1157 = 34^2 + 1 = 13*89 and the numbers 13, 89 are not of the form 1 plus a square.

MAPLE

isA217279 := proc(n)

    if issqr(n-1) then

        for d in numtheory[factorset](n) do

            if issqr(d-1) then

                return false;

            end if;

        end do:

        return true ;

    else

        false;

    end if;

end proc:

for n from 1 to 300 do

    if isA217279(n^2+1) then

        printf("%d ", n^2+1) ;

    end if;

end do: # R. J. Mathar, Oct 01 2012

MATHEMATICA

Select[1 + Range[400]^2, Not[PrimeQ[#]] && Intersection[Divisors[#], 1 + Range[Sqrt[# - 1] - 1]^2] == {} &] (* Alonso del Arte, Sep 29 2012 *)

CROSSREFS

Cf. A002522, A005574, A217276, A181436, A180252.

Sequence in context: A264271 A264089 A264278 * A204478 A031746 A219148

Adjacent sequences:  A217276 A217277 A217278 * A217280 A217281 A217282

KEYWORD

nonn

AUTHOR

Michel Lagneau, Sep 29 2012

STATUS

approved

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 April 14 21:21 EDT 2021. Contains 342962 sequences. (Running on oeis4.)