Number Series

Aptitude

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Number series is an important chapter in an aptitude section. A number series is basically a sequence of numbers written in a certain order or pattern. And to solve these kinds of problems we have to find the pattern followed in the sequence.

Some of the most common series are discussed here.

Arithmetic Progression (A.P.) Series

Arithmetic Progression or A.P. series are a sequence of numbers in which the difference between any two consecutive numbers is always the same.

A.P. series is of the form a, a+d, a+2d, a+3d …

Where, a is the first term and d is the common difference.

Common difference is calculated by subtracting the 2nd term from the 1st term.

The nth term in this series is denoted as Tn = a + (n-1)d

Set of even numbers is an example of A.P. series.

E = {2, 4, 6, 8, 10 …}

Here the first term a = 2 and the common difference d = 2.

 

Geometric Progression (G.P.) Series

Geometric Progression or G.P. series are a sequence of numbers in the ratio of any two consecutive numbers is the same.

G.P. series is denoted as a, ar, ar2, ar3

Where, a is the first term and r is the common ration.

Common ration is calculated by dividing the 2nd term by the 1st term.

The nth term of a G.P. series is denoted by Tn = arn-1

X = {2, 4, 8, 16, 32, 64, 128, 256 …}

X is an example of G.P. series. The first term a = 2 and the common ratio r = 4/2 = 2

 

Even number series

This is a series consisting of even numbers. This is also an example of A.P. series. The terms of this series is denoted as x, x+2, x+4, x+6 … where x is the first even number in the series.

Example 2, 4, 6, 8 … is an even number series.

 

Odd number series

This is a series consisting of odd numbers. This is also an example of A.P. series. The terms of this series is denoted as x, x+2, x+4, x+6 … where x is the first odd number in the series.

Example 1, 3, 5, 7 … is an odd number series.

 

Prime number series

This is a series consisting of prime numbers.

Example 2, 3, 5, 7, 11 …

 

Square series

This is a series consisting of square of numbers. The terms of this series is denoted as n2.

Example 1, 4, 9, 16, 25 … is a square series consisting of the square of the natural numbers.

 

Cube series

This is a series consisting of cube of numbers. The terms of this series is denoted as n3.

Example 1, 8, 27, 64, 125 … is a cube series consisting of the cube of the natural numbers.

 

Fibonacci series

This is a series that follows the given rules

T0 = 1 and T1 = 1

Tn = Tn-1 + Tn-2 for all values of n >= 2

The first and second term is taken as 1 while any other term is equal to the sum of two previous terms.

Example 1, 1, 2, 3, 5, 8, 13, 21 … is a fibonacci series.

 

n2+1 series

This is a series consisting of squares plus 1 of numbers.

Example 2, 5, 10, 17, 26 … is a n2+1 series of natural numbers.

 

n3+1 series

This is a series consisting of cube plus 1 of numbers.

Example 2, 9, 28, 65, 126 … is a n3+1 series of natural numbers.

 

n2-1 series

This is a series consisting of squares minus 1 of numbers.

Example 0, 3, 8, 15, 24 … is a n2-1 series of natural numbers.

 

n3-1 series

This is a series consisting of cube minus 1 of numbers.

Example 0, 7, 26, 63, 124 … is a n3-1 series of natural numbers.