25643985470955911102

This number is a composite.

                                                       2564398547 0955911102

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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]