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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 (list; graph; refs; listen; history; text; internal format)
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

Robert Israel, Table of n, a(n) for n = 1..10000

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

Cf. A000217, A061304, A021913.

Sequence in context: A323511 A284391 A127015 * A286749 A188192 A068432

Adjacent sequences:  A281111 A281112 A281113 * A281115 A281116 A281117

KEYWORD

nonn

AUTHOR

Rick L. Shepherd, Jan 14 2017

STATUS

approved

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Last modified October 15 01:40 EDT 2019. Contains 328025 sequences. (Running on oeis4.)