Primality Test | Set 5 ( Using Lucas | Function to check whether ( 2 ^ p - 1 ) is prime or not . ; generate the number ; First number of the series ; Generate the rest ( p - 2 ) terms of the series . ; now if the ( p - 1 ) th term is 0 return true else false . ; Check whether 2 ^ p - 1 is prime or not .
function isPrime ( p ) { let checkNumber = Math . pow ( 2 , p ) - 1 ; let nextval = 4 % checkNumber ; for ( let i = 1 ; i < p - 1 ; i ++ ) nextval = ( nextval * nextval - 2 ) % checkNumber ; return ( nextval == 0 ) ; } let p = 7 ; let checkNumber = Math . pow ( 2 , p ) - 1 ; if ( isPrime ( p ) ) document . write ( checkNumber + " " ) ; else document . write ( checkNumber + " " ) ;