642787821 has 24 divisors (see below), whose sum is σ = 1032152576. Its totient is φ = 382799520.

The previous prime is 642787819. The next prime is 642787829. The reversal of 642787821 is 128787246.

It is not a de Polignac number, because 642787821 - 2¹ = 642787819 is a prime.

It is a super-3 number, since 3×642787821³ (a number of 27 digits) contains 333 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (642787829) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 84985 + ... + 92238.

Almost surely, 2^642787821 is an apocalyptic number.

It is an amenable number.

642787821 is a deficient number, since it is larger than the sum of its proper divisors (389364755).

642787821 is a wasteful number, since it uses less digits than its factorization.

642787821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 177273 (or 177270 counting only the distinct ones).

The product of its digits is 301056, while the sum is 45.

The square root of 642787821 is about 25353.2605595414. The cubic root of 642787821 is about 863.0233506802.

The spelling of 642787821 in words is "six hundred forty-two million, seven hundred eighty-seven thousand, eight hundred twenty-one".