25643985470955911102

This number is a composite.

                                                       2564398547 0955911102

The only known multidigit nonprime solution n to the Subbarao's congruence ϕ(n) × tau(n) + 2 == 0 (mod n), a property trivially satisfied by all primes. Here, ϕ(n) refers to the totient function and tau(n) refers to the number of divisors. [Gudipati]