A334320 Number of even integers in base n with exactly two distinct digits.

0, 0, 1, 1, 5, 6, 13, 15, 25, 28, 41, 45, 61, 66, 85, 91, 113, 120, 145, 153, 181, 190, 221, 231, 265, 276, 313, 325, 365, 378, 421, 435, 481, 496, 545, 561, 613, 630, 685, 703, 761, 780, 841, 861, 925, 946, 1013, 1035, 1105, 1128, 1201, 1225, 1301, 1326, 1405

Offset: 0

Author

Alois P. Heinz, Apr 22 2020

Keywords

• nonn
• easy

Examples

			a(4) = 5: 10, 12, 20, 30, 32 (written in base 4).
a(7) = 15: 13, 15, 20, 24, 26, 31, 35, 40, 42, 46, 51, 53, 60, 62, 64 (written in base 7).
		

Links

• Alois P. Heinz, Table of n, a(n) for n = 0..10000
• Index entries for linear recurrences with constant coefficients, signature (1,2,-2,-1,1).

Crossrefs

Column k=2 of A334318.

Formula

G.f.: -(x^3+2*x^2+1)*x^2/((x+1)^2*(x-1)^3).

a(n) = A334318(n,2).