This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
p = Select[Prime[Range[250]], !SquareFreeQ[#^2+1]&]; p^2 * (p^2+1)
23 is a term since 23^2+1 = 530 = 2*5*53, is squarefree. 43 is not a term since 43^2+1 = 1850 = 2*5^2*7, is not squarefree.
Select[Prime[Range[100]], SquareFreeQ[#^2+1]&]
38 = 2*19 is squarefree but 38*38 + 1 = 1445 = 5*17*17 is not squarefree.
filter:= proc(n) numtheory:-issqrfree(n) and not numtheory:-issqrfree(n^2+1) end proc: select(filter, [$1..1000]); # Robert Israel, May 04 2025
Select[Range[900],SquareFreeQ[#] && !SquareFreeQ[#^2+1] &] (* Stefano Spezia, May 04 2025 *)
isok(k) = issquarefree(k) && !issquarefree(k^2+1); \\ Michel Marcus, May 04 2025
from sympy import factorint
def is_squarefree(n):
return all(exponent == 1 for exponent in factorint(n).values())
print([a for a in range(1,900) if is_squarefree(a) and not(is_squarefree(a*a + 1))])
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