#!/bin/ksh

# Increment loop index within loop body

#   # Variables:
#
integer INDX_START=42 N_PRIMES=42

#   # Functions:
#

#   # Function _isprime(n) return 1 for prime, 0 for not prime
#
function _isprime {
    typeset _n ; integer _n=$1
    typeset _i ; integer _i

    (( _n < 2 )) && return 0
    for (( _i=2 ; _i*_i<=_n ; _i++ )); do
        (( ! ( _n % _i ) )) && return 0
    done
    return 1
}

 ######
# main #
 ######
integer i n=0
for ((i=INDX_START; n<N_PRIMES; i++)); do
    _isprime ${i}
    if (( $? )); then
        printf "%,18d is prime, %2d primes found(so far)\n" ${i} $((++n))
        (( i+=$i ))
    fi
done