Complex sentence: He has found many large prime numbers of special forms: repunits, prime Fibonacci and Lucas numbers, twin primes, Sophie Germain primes, primes in arithmetic progression; in 1993 he was responsible for more than half the known primes of more than two thousand digits.
Split into simpler sentences: He has found many large prime numbers of special forms: repunits, prime Fibonacci and Lucas numbers, twin primes, Sophie Germain primes, and primes in arithmetic progression. In 1993 he was responsible for more than half the known primes of more than two thousand digits.