OFFSET
1,1
COMMENTS
Or, (odd integers n such that) n^2 + 4 is not squarefree. - Zak Seidov, Feb 03 2013
LINKS
Ruskin Harding, Table of n, a(n) for n = 1..5258
EXAMPLE
The first odd value of k for which k^2+4 has a square factor is 11: 11^2+4 = 125 = 5^2*5.
MATHEMATICA
Select[Range[11, 1000, 2], ! SquareFreeQ[#^2 + 4] &] (* Zak Seidov, Feb 03 2013 *)
PROG
(Python)
b=1
x=1
for i in range(1, 100000, 2):
....for j in range(2, i):
.......if ((i**2)+4)%(j**2)==0:
..........a=i
..........if a!=b:
.............b=a
.............print(x, i)
.............x=x+1
(PARI)
is_term(n) = !issquarefree(n^2+4);
forstep (n=1, 10^3, 2, if (is_term(n), print1(n, ", ")));
/* Joerg Arndt, Feb 05 2013 */
(Magma) [k: k in [1..1000 by 2] | not IsSquarefree(k^2+4)]; // Bruno Berselli, Feb 06 2013
CROSSREFS
KEYWORD
nonn
AUTHOR
Ruskin Harding, Feb 03 2013
EXTENSIONS
b-file calculated to more decimal places.
Python program improved.
STATUS
approved