A117872 Parity of the iterated triangular numbers, using "2" as a seed.

0, 1, 0, 1, 1, 0, 0, 1, 1, 1, 1, 0, 0, 1, 0, 1, 1, 1, 0, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 1, 0, 0, 1, 1, 1, 0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 0, 1, 1, 0, 0, 1, 1, 1, 0, 0, 0, 1, 0, 1, 0, 1, 1, 1, 1, 0, 1, 1, 0, 1, 1, 1, 1, 0, 0, 1, 1, 1, 0, 1, 1, 0, 0, 1, 0, 1, 0, 0, 0, 1, 1, 1

Offset

0,1

Comments

Suggested by D. R. Hofstadter.

a(n) = A007501(n) mod 2.

Links

Charles R Greathouse IV, Table of n, a(n) for n = 0..10000

Formula

a(n) = mod(T^(n)(2), 2)

Example

a(1) = mod(T(2),2) = mod(3, 2) = 1.
a(4) = mod(T(T(T(T(2)))),2) = mod(231,2) = 1.

Prog

(Haskell)
a117872 = flip mod 2 . a007501  -- Reinhard Zumkeller, Aug 15 2013
(PARI) list(n)=my(t=Mod(2, 2*2^n)); concat(0, vector(n, i, t*=t+1; t=Mod(lift(t)/2, t.mod/2); lift(Mod(t, 2)))) \\ Charles R Greathouse IV, Aug 22 2013

Crossrefs

Cf. A007501, A126768

Sequence in context: A165221 A295891 A093879 * A291291 A324681 A368909

Adjacent sequences: A117869 A117870 A117871 * A117873 A117874 A117875

Keyword

easy,nonn

Author

Greg Huber, May 13 2006, Feb 16 2007

Extensions

More terms from Greg Huber, Feb 16 2007

a(38) and on corrected by Greg Huber, Aug 21 2013

Status

approved