A066755 Numbers n such that n^2 + 1 is not divisible by k^2 + 1 for any k in [1,n-1].

1, 2, 4, 6, 10, 14, 16, 20, 24, 26, 34, 36, 40, 44, 46, 50, 54, 56, 60, 66, 70, 74, 76, 84, 86, 90, 94, 96, 100, 104, 110, 114, 116, 120, 124, 126, 130, 134, 136, 144, 146, 150, 156, 160, 164, 170, 176, 180, 184, 186, 190, 194, 196, 204, 206, 210, 214, 220, 224

Offset

1,2

Comments

Equivalently, A066743(n)=1.

If n^2 + 1 is prime, n is in the sequence; i.e., the sequence contains A005574. But so are many other values of n: 34,44,46,50,60,70,76,86,96,...

Links

Harry J. Smith, Table of n, a(n) for n = 1..1000

Maple

a:= proc(n) option remember; local k; for k from 1+
      `if`(n=1, 0, a(n-1)) while ormap(t->
      irem(k^2+1, t)=0, [(j^2+1)$j=1..k-1]) do od; k
    end:
seq(a(n), n=1..100);  # Alois P. Heinz, Sep 18 2019

Mathematica

a66743[ n_ ] := Length[ Select[ Range[ 1, n ], IntegerQ[ (n^2+1)/(#^2+1) ]& ] ]; Select[ Range[ 1, 300 ], a66743[ # ]==1& ]

Prog

(PARI) { n=0; for (m=1, 10^10, k=1; b=1; t=m^2 + 1; while (k < m - 1, if (t%(k^2 + 1)==0, b=0; break); k++); if (b, write("b066755.txt", n++, " ", m); if (n==1000, return)) ) } \\ Harry J. Smith, Mar 23 2010

Crossrefs

Cf. A066743, A005574.

Sequence in context: A325418 A075574 A104692 * A089238 A005574 A109807

Adjacent sequences: A066752 A066753 A066754 * A066756 A066757 A066758

Keyword

nonn

Author

Benoit Cloitre, Jan 16 2002

Extensions

Edited by Dean Hickerson, Jan 20 2002

Status

approved