A155721 Positions of parity change in A033035.

4, 20, 84, 340, 1364, 5460, 21844, 87380, 349524, 1398100, 5592404, 22369620, 89478484, 357913940, 1431655764, 5726623060, 22906492244, 91625968980, 366503875924, 1466015503700, 5864062014804, 23456248059220, 93824992236884

Offset: 1

Author

Zak Seidov, Jan 25 2009

Keywords

• nonn

Comments

Numbers n such that A033035(n)=(7/8)*(9^n - 1)=7*A002452(n).

Examples

			A033035(n=1..4) all are odd, then A033035(n=5..20) all are even, then A033035(n=21..84) all are odd, then A033035(n=85..340) all are even, etc.
		

Crossrefs

A002452, A033035, A080674.

Formula

a(n=1,2..)=(4/3)*(4^n-1)=A080674(n).

a(n) = 5*a(n-1) - 4*a(n-2) for n > 2. G.f.: 4*x/((x - 1)*(4*x - 1)). - Chai Wah Wu, Aug 30 2019