OFFSET
1,1
COMMENTS
Probably 11*n < a(n) < 12*n for n > 189. - Charles R Greathouse IV, Nov 05 2017
The asymptotic density of this sequence is 1/zeta(2) - 2 * Product_{p prime} (1 - 2/p^2) + Product_{p prime} (1 - 3/p^2) = A059956 - 2*A065474 + A206256 = 0.088145884881346585838... . - Amiram Eldar, Aug 30 2024
LINKS
Christopher E. Thompson, Table of n, a(n) for n = 1..10000
MAPLE
sf:= select(numtheory:-issqrfree, [$1..1000]):
map(t -> `if`(sf[t-1]=sf[t]-1 or sf[t+1]=sf[t]+1, NULL, sf[t]), [$2..nops(sf)-1]); # Robert Israel, Feb 01 2016
MATHEMATICA
Reap[For[n = 0, n <= 1000, n++, If[SquareFreeQ[n] && !SquareFreeQ[n-1] && !SquareFreeQ[n+1], Sow[n]]]][[2, 1]] (* Jean-François Alcover, Feb 26 2019 *)
PROG
(PARI) is(n)=!issquarefree(n-1) && issquarefree(n) && !issquarefree(n+1) \\ Charles R Greathouse IV, Nov 05 2017
CROSSREFS
KEYWORD
nonn
AUTHOR
Reinhard Zumkeller, Jul 22 2002
STATUS
approved