684921221 has 2 divisors, whose sum is σ = 684921222. Its totient is φ = 684921220.

The previous prime is 684921199. The next prime is 684921227. The reversal of 684921221 is 122129486.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 512524321 + 172396900 = 22639^2 + 13130^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-684921221 is a prime.

It is a super-2 number, since 2×684921221² = 938234157952261682, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (684921227) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 342460610 + 342460611.

It is an arithmetic number, because the mean of its divisors is an integer number (342460611).

Almost surely, 2^684921221 is an apocalyptic number.

It is an amenable number.

684921221 is a deficient number, since it is larger than the sum of its proper divisors (1).

684921221 is an equidigital number, since it uses as much as digits as its factorization.

684921221 is an evil number, because the sum of its binary digits is even.

The product of its digits is 13824, while the sum is 35.

The square root of 684921221 is about 26170.9996178977. Note that the first 3 decimals coincide. The cubic root of 684921221 is about 881.4821874919.

The spelling of 684921221 in words is "six hundred eighty-four million, nine hundred twenty-one thousand, two hundred twenty-one".