684787021 has 2 divisors, whose sum is σ = 684787022. Its totient is φ = 684787020.

The previous prime is 684786989. The next prime is 684787031. The reversal of 684787021 is 120787486.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 372876100 + 311910921 = 19310^2 + 17661^2 .

It is a cyclic number.

It is not a de Polignac number, because 684787021 - 2⁵ = 684786989 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (684787031) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 342393510 + 342393511.

It is an arithmetic number, because the mean of its divisors is an integer number (342393511).

Almost surely, 2^684787021 is an apocalyptic number.

It is an amenable number.

684787021 is a deficient number, since it is larger than the sum of its proper divisors (1).

684787021 is an equidigital number, since it uses as much as digits as its factorization.

684787021 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 150528, while the sum is 43.

The square root of 684787021 is about 26168.4355856440. The cubic root of 684787021 is about 881.4246126776.

The spelling of 684787021 in words is "six hundred eighty-four million, seven hundred eighty-seven thousand, twenty-one".