A note on square totients

Tristan Freiberg, Carl Pomerance
2015 International Journal of Number Theory  
A well-known conjecture asserts that there are infinitely many primes p for which p - 1 is a perfect square. We obtain upper and lower bounds of matching order on the number of pairs of distinct primes p,q < x for which (p - 1)(q - 1) is a perfect square.
doi:10.1142/s179304211550102x fatcat:oivw3zblnfek3gel7iywiars7a