

A134427


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


2



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
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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 A085722 A023980
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



