A268955 Number of length-n 0..7 arrays with no repeated value equal to the previous repeated value, with new values introduced in sequential order.

1, 2, 4, 12, 40, 154, 656, 3074, 15615, 85314, 497262, 3068890, 19899645, 134520386, 940841796, 6760952170, 49617422739, 370013347266, 2792665457338, 21266237427018, 163008076378489, 1255477313622210, 9703388630792784

Offset: 1

Author

R. H. Hardin, Feb 16 2016

Keywords

• nonn

Comments

Column 7 of A268956.

Examples

			Some solutions for n=8
..0. .0. .0. .0. .0. .0. .0. .0. .0. .0. .0. .0. .0. .0. .0. .0
..1. .0. .1. .0. .1. .1. .0. .1. .1. .0. .1. .1. .0. .1. .1. .1
..2. .1. .2. .1. .2. .1. .1. .0. .2. .1. .2. .2. .1. .0. .2. .0
..0. .2. .2. .0. .0. .0. .2. .2. .3. .2. .3. .1. .1. .2. .0. .2
..1. .3. .1. .2. .2. .2. .1. .3. .4. .3. .3. .2. .2. .0. .3. .3
..2. .4. .0. .1. .1. .3. .3. .0. .5. .2. .4. .3. .0. .1. .2. .0
..2. .1. .3. .2. .3. .0. .4. .3. .2. .4. .2. .1. .2. .3. .2. .4
..3. .1. .1. .0. .1. .1. .2. .3. .6. .5. .4. .2. .1. .0. .4. .2
		

Links

• R. H. Hardin, Table of n, a(n) for n = 1..210

Crossrefs

Cf. A268956.

Formula

Empirical: a(n) = 38*a(n-1) -593*a(n-2) +4702*a(n-3) -17263*a(n-4) -4158*a(n-5) +265149*a(n-6) -681270*a(n-7) -916836*a(n-8) +6212496*a(n-9) -2473032*a(n-10) -24948000*a(n-11) [phone]*a(n-12) [phone]*a(n-13) -73975984*a(n-14) -60452512*a(n-15) [phone]*a(n-16) [phone]*a(n-17) -45158400*a(n-18) for n>20