A134427 - OEIS

A134427

Numbers k such that k^2 + 1 is a composite squarefree number.

3, 5, 8, 9, 11, 12, 13, 15, 17, 19, 21, 22, 23, 25, 27, 28, 29, 30, 31, 33, 34, 35, 37, 39, 42, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 55, 58, 59, 60, 61, 62, 63, 64, 65, 67, 69, 71, 72, 73, 75, 76, 77, 78, 79, 80, 81, 83, 85, 86, 87, 88, 89, 91, 92, 95, 96, 97, 98, 100, 101

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

LINKS

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

EXAMPLE

a(1)=3, because 3^2 + 1 = 10 is composite squarefree.

a(2)=5, because 5^2 + 1 = 26 is composite squarefree.

a(3)=8, because 8^2 + 1 = 50 is composite squarefree.

MAPLE

ts_fn4:=proc(n) local i, tren, ans; ans:=[ ]: for i from 1 to n do tren := i^(2)+1: if (isprime(tren) = false and numtheory[mobius] (tren) <> 0 ) then ans:=[ op(ans), i ]: fi od: RETURN(ans) end: ts_fn4(200);

MATHEMATICA

Select[Range[100], CompositeQ[#^2+1] && SquareFreeQ[#^2+1] &] (* Amiram Eldar, Feb 22 2021 *)

CROSSREFS

Cf. A002496, A124809, A134420.

Sequence in context: A189288 A190205 A192884 * A065347 A376428 A085722

Adjacent sequences: A134424 A134425 A134426 * A134428 A134429 A134430

KEYWORD

nonn

AUTHOR

Jani Melik, Jan 18 2008

EXTENSIONS

Definition corrected by T. D. Noe, Sep 16 2008

STATUS

approved