684253721 has 2 divisors, whose sum is σ = 684253722. Its totient is φ = 684253720.

The previous prime is 684253709. The next prime is 684253727. The reversal of 684253721 is 127352486.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 582546496 + 101707225 = 24136^2 + 10085^2 .

It is a cyclic number.

It is not a de Polignac number, because 684253721 - 2¹⁸ = 683991577 is a prime.

It is not a weakly prime, because it can be changed into another prime (684253727) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 342126860 + 342126861.

It is an arithmetic number, because the mean of its divisors is an integer number (342126861).

Almost surely, 2^684253721 is an apocalyptic number.

It is an amenable number.

684253721 is a deficient number, since it is larger than the sum of its proper divisors (1).

684253721 is an equidigital number, since it uses as much as digits as its factorization.

684253721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 80640, while the sum is 38.

The square root of 684253721 is about 26158.2438439586. The cubic root of 684253721 is about 881.1957406292.

The spelling of 684253721 in words is "six hundred eighty-four million, two hundred fifty-three thousand, seven hundred twenty-one".