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# Index to OEIS: Section O

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# Index to OEIS: Section O

- This is a section of the Index to the
**OEIS®**. - For further information see the main
**Index to OEIS**page. - Please read Index: Instructions For Updating Index to OEIS before making changes to this page.
- If you did not find what you were looking for in this Index, you can always search the database for a particular word or phrase.
- Full list of sections:

[
Aa |
Ab |
Al |
Am |
Ap |
Ar |
Ba |
Be |
Bi |
Bl |
Bo |
Br |
Ca |
Ce |
Ch |
Cl |
Coa |
Coi |
Com |
Con |
Cor |
Cu |
Cy |
Da |
De |
Di |
Do |
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Ed |
El |
Eu |
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Fe |
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He |
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La |
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Pac |
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Poi |
Pol |
Pos |
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Pra |
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Rea |
Rel |
Res |
Ro |
Ru |
Sa |
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Tri |
Tu |
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]

O'Nan group: A003919, A008625

obtaining numbers from other numbers and the operations of addition, subtraction, etc: see under four 4's problem

octagonal numbers: A000567*

octahedral numbers: A005900*

octahedron, truncated: see truncated octahedron

octahedron: A005899

** octal numbers, sequences related to : **

octupi: A029767*

** odd numbers , sequences related to : **

- odd numbers n such that 2^k + n is composite for all k: see A076336
- odd numbers, fake: A080591
- odd numbers: A005408*
- odd numbers: see also A000700, A000069, A007697, A006046, A007455, A007482, A000593, A007483, A006945, A001033, A002309, A006285, A002594, A006038

odd unimodular lattices, see: lattices, unimodular

odious numbers: A000069*

omega(n), number of distinct primes dividing n: A001221

Omega(n), total number of primes dividing n: A001222

one local maximum, arrays with: A007846, A000079, A087518, A087783*, A087923-A087932

one odd, two even, etc.: A001614

one puddle: see one local maximum

ones-counting sequence: A000120

open problems: see also unsolved problems in number theory (selected)

open problems: try searching in the OEIS for the following words: conjecture, apparently, appears, seems, probably, etc.

operational recurrences: A001577*

Opmanis's nice base-dependent sequence: A177834

optimal rulers: see perfect rulers

OR(x,y): A003986*

OR: A007460, A006583

orchard problem: A003035*, A006065, A008997

** order or orders, sequences related to : **

- order, binary: A029837
- order, multiplicative order of 2 mod n: A002326
- order, ord(x,y): the multiplicative order of x mod y, see entries under: multiplicative order
- order: see also under multiplicative order
- ordered factorizations: A074206*, A002033
- ordered partitions: see also under partitions
- orders, total: see total orders
- orders, weak: A000790
- orders: A000670, A004123, A004122, A004121
- orders: see also hierarchies

ordinals: A005348

Ore numbers: A001599*, A001600

** orthogonal arrays, sequences related to : **

- orthogonal arrays, number of: A039931*, A039927*, A048885*
- orthogonal arrays, see also: A008286, A039930, A048164, A048638, A048893, A049082, A049083

orthogonal groups: A003053*, A001051

out-points: A003025, A003026

overpartitions: A015128

- This is a section of the Index to the
**OEIS®**. - For further information see the main
**Index to OEIS**page. - Please read Index: Instructions For Updating Index to OEIS before making changes to this page.
- If you did not find what you were looking for in this Index, you can always search the database for a particular word or phrase.
- Full list of sections:

[
Aa |
Ab |
Al |
Am |
Ap |
Ar |
Ba |
Be |
Bi |
Bl |
Bo |
Br |
Ca |
Ce |
Ch |
Cl |
Coa |
Coi |
Com |
Con |
Cor |
Cu |
Cy |
Da |
De |
Di |
Do |
Ea |
Ed |
El |
Eu |
Fa |
Fe |
Fi |
Fo |
Fu |
Ga |
Ge |
Go |
Gra |
Gre |
Ha |
He |
Ho |
Ia |
In |
J |
K |
La |
Lc |
Li |
Lo |
Lu |
M |
Mag |
Map |
Mat |
Me |
Mo |
Mu |
N |
Na |
Ne |
Ni |
No |
Nu |
**O** |
Pac |
Par |
Pas |
Pea |
Per |
Ph |
Poi |
Pol |
Pos |
Pow |
Pra |
Pri |
Pro |
Ps |
Qua |
Que |
Ra |
Rea |
Rel |
Res |
Ro |
Ru |
Sa |
Se |
Si |
Sk |
So |
Sp |
Sq |
St |
Su |
Sw |
Ta |
Te |
Th |
To |
Tra |
Tri |
Tu |
U |
V |
Wa |
We |
Wi |
X |
Y |
Z |
1 |
2 |
3 |
4
]