Prime number is a number that cannot be divided without remainder except 1 or itself.  

Whether a number is prime or not is pre-determined, and mathematicians don’t have a consistent way to predict which numbers are prime, and so tend to treat them as if they occur randomly. 

However Kannan Soundararajan and Robert Lemke Oliver of Stanford University in California have discovered some patterns. 

Apart from 2 and 5, all prime numbers end in 1, 3, 7 or 9 – they have to, else they would be divisible by 2 or 5 – and each of the four endings is equally likely. But while searching through the primes, the two mathematicians noticed that primes ending in 1 were less likely to be followed by another prime ending in 1. That shouldn’t happen if the primes were truly random –  consecutive primes shouldn’t care about their neighbour’s digits.

The pair found that in the first hundred million primes, a prime ending in 1 is followed by another ending in 1 just 18.5% of the time. If the primes were distributed randomly, you’d expect to see two 1s next to each other 25 per cent of the time. Primes ending in 3 and 7 each following a 1 in 30% of primes, while a 9 follows a 1 in around 22%  of occurrences.
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