A167154 Numbers where terms in A167153 change parity: a(n)+1 is in A167153, but a(n)-1 is not.

9, 30, 49, 70, 89, 200, 399, 600, 799, 1000

Offset

1,1

Comments

Sequence A167153 consists of runs of numbers of the same parity. It is conjectured that each time the parity changes, there is a gap of 3 numbers, and the sequence goes on with the successor a(n)+1 (of opposite parity) of the first "missing" term a(n) in the run of terms of given parity (a(n-1)+1, a(n-1)+3, ..., a(n)-2).

Links

Table of n, a(n) for n=1..10.

E. Angelini, a(n) is the digitsum of a(a(n)), November 2009.

E. Angelini, a(n) is the digitsum of a(a(n)) [Cached copy, with permission]

Example

Sequence A167153 starts 10,12,14,... so a(1)=9 is the predecessor of the first even term 10 = a(1)+1 in the sequence.
Then the sequence changes parity at ...,26, 28, 31, 33,..., i.e. a(2)-2 = 28 is the last term in this run of even numbers, a(2) = 30 is missing, and the sequence goes on with odd numbers starting at a(2)+1 = 31.
That run of odd numbers ends with a(3)-2 = 47; a(3) = 49 is missing, and the sequence goes on with even numbers starting at a(3)+1 = 50.

Crossrefs

Cf. A167152. A167153.

Sequence in context: A179506 A185653 A326150 * A063150 A063161 A295867

Adjacent sequences: A167151 A167152 A167153 * A167155 A167156 A167157

Keyword

more,nonn,base

Author

Eric Angelini and M. F. Hasler, Nov 03 2009

Status

approved