# GeetCode Hub

Given an integer array `nums`, return the number of all the arithmetic subsequences of `nums`.

A sequence of numbers is called arithmetic if it consists of at least three elements and if the difference between any two consecutive elements is the same.

• For example, `[1, 3, 5, 7, 9]`, `[7, 7, 7, 7]`, and `[3, -1, -5, -9]` are arithmetic sequences.
• For example, `[1, 1, 2, 5, 7]` is not an arithmetic sequence.

A subsequence of an array is a sequence that can be formed by removing some elements (possibly none) of the array.

• For example, `[2,5,10]` is a subsequence of `[1,2,1,2,4,1,5,10]`.

The answer is guaranteed to fit in 32-bit integer.

Example 1:

```Input: nums = [2,4,6,8,10]
Output: 7
Explanation: All arithmetic subsequence slices are:
[2,4,6]
[4,6,8]
[6,8,10]
[2,4,6,8]
[4,6,8,10]
[2,4,6,8,10]
[2,6,10]
```

Example 2:

```Input: nums = [7,7,7,7,7]
Output: 16
Explanation: Any subsequence of this array is arithmetic.
```

Constraints:

• `1  <= nums.length <= 1000`
• `-231 <= nums[i] <= 231 - 1`

class Solution { public int numberOfArithmeticSlices(int[] nums) { } }
Medium