A193414 - OEIS

A193414

Numbers m such that written in base 2 the structure of digits represents a valley.

1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 23, 25, 27, 29, 31, 33, 35, 39, 47, 49, 51, 55, 57, 59, 61, 63, 65, 67, 71, 79, 95, 97, 99, 103, 111, 113, 115, 119, 121, 123, 125, 127, 129, 131, 135, 143, 159, 191, 193, 195, 199, 207, 223, 225, 227, 231, 239, 241, 243

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OFFSET

1,2

COMMENTS

For n > 1 the structure of digits of numbers written in base 2 represents a valley. The first digit is equal to the last digit (1). The first digits are in nonincreasing order. The last digits are in nondecreasing order. The numbers may have more than one 0 digit. Sequence is infinite.

See A193415: numbers m written in base 2: {1, 11, 101, 111, 1001, 1011, 1101, 1111, ...}.

LINKS

Table of n, a(n) for n=1..59.

EXAMPLE

Illustration using 67 = 1000011_2:

1 . . . . 1 1

. 0 0 0 0 . .

MATHEMATICA

Select[Range[300], MemberQ[{1, 3}, Length[Split[IntegerDigits[#, 2]]]] &] (* T. D. Noe, Jul 26 2011 *)

CROSSREFS

Cf. A193413 (Valley numbers written in base 10), A193415.

Sequence in context: A372293 A288452 A338316 * A138217 A074775 A356845