A171781 Numbers for which the second bit of the binary expansion is equal to the last bit.

2, 3, 4, 7, 8, 10, 13, 15, 16, 18, 20, 22, 25, 27, 29, 31, 32, 34, 36, 38, 40, 42, 44, 46, 49, 51, 53, 55, 57, 59, 61, 63, 64, 66, 68, 70, 72, 74, 76, 78, 80, 82, 84, 86, 88, 90, 92, 94, 97, 99, 101, 103, 105, 107, 109, 111, 113, 115, 117, 119, 121, 123, 125

Offset: 1

Author

N. J. A. Sloane, Oct 12 2010

Keywords

• nonn
• base

Comments

Note that A005843 INTERSECT A171781 = A171757. This is an example of two sequences which both have a limiting density, but whose intersection does not.

Examples

			10 is a term since its binary representation is 1010 and both its second and last bits are 0. - _Amiram Eldar_, Sep 01 2020
		

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A005843, A171782, A171757, A171763.

Programs

Mathematica

Select[Range[2, 125], (d = IntegerDigits[#, 2])[[2]] == d[[-1]] &] (* Amiram Eldar, Sep 01 2020 *)