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A281114
Parity of the n-th squarefree triangular number.
1
1, 1, 0, 0, 1, 1, 1, 0, 0, 1, 1, 0, 0, 1, 1, 0, 1, 1, 1, 1, 1, 1, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 1, 1, 0, 0, 1, 1, 1, 0, 1, 1, 1, 0, 0, 1, 1, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 0, 1, 1, 0, 0, 1, 1, 1, 0, 0, 1, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 1, 0, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 0, 0, 1, 1, 1
OFFSET
1
COMMENTS
The sequence giving the parity of all triangular numbers is periodic with period 4 after the initial 0, A000217(n) mod 2 = A021913(n+1).
LINKS
FORMULA
a(n) = A061304(n) mod 2.
EXAMPLE
The eighth squarefree triangular number is 66, which is even, so a(8) = 0.
MAPLE
map(t -> `if`(t-1 mod 4 <= 1, 1, 0), select(t -> numtheory:-issqrfree(t*(t+1)/2), [$1..1000])); # Robert Israel, Oct 09 2017
MATHEMATICA
Boole@ OddQ@ # & /@ Select[PolygonalNumber@ Range@ 210, SquareFreeQ] (* Michael De Vlieger, Oct 06 2017 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Rick L. Shepherd, Jan 14 2017
STATUS
approved