# NumPy Project Euler Problem 1

This entry is part 1 of 9 in the series NumPy Project Euler

Project Euler is a website that lists a number of mathematical problems, which are perfect to be solved with NumPy. Let’s start the new year with Problem 1.

### 1. Call the arange function

Call the arange function in order to store all the integers from 1 to 1000 in an array.

```# 1. Numbers 1 - 1000 a = numpy.arange(1, 1000)```

### 2. Select the multiples of 3 or 5

Select using the [] operator.

```# 2. Select multiple of 3 or 5 a = a[(a % 3 == 0) | (a % 5 == 0)] print a[:10]```

This prints as expected

`[ 3 5 6 9 10 12 15 18 20 21]`

### 3. Sum the array elements

Call the sum method on the NumPy array.

```# 3. Sum the numbers print a.sum()```

Once again the code below in its entirety.

```import numpy   #Problem 1. #If we list all the natural numbers below 10 that are multiples of 3 or 5, we get 3, 5, 6 and 9. #The sum of these multiples is 23.   #Find the sum of all the multiples of 3 or 5 below 1000.   # 1. Numbers 1 - 1000 a = numpy.arange(1, 1000)   # 2. Select multiple of 3 or 5 a = a[(a % 3 == 0) | (a % 5 == 0)] print a[:10]   # 3. Sum the numbers print a.sum()```

If you liked this post and are interested in NumPy check out NumPy Beginner’s Guide by yours truly.

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