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

Author

Greg Huber, May 13 2006, Feb 16 2007

Keywords

• easy
• nonn

Comments

Suggested by D. R. Hofstadter.

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

Examples

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

Links

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

Crossrefs

Cf. A007501, A126768

Programs

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

Formula

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

Extensions

More terms from Greg Huber, Feb 16 2007

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