721621421 has 2 divisors, whose sum is σ = 721621422. Its totient is φ = 721621420.

The previous prime is 721621393. The next prime is 721621427. The reversal of 721621421 is 124126127.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 700184521 + 21436900 = 26461^2 + 4630^2 .

It is a cyclic number.

It is not a de Polignac number, because 721621421 - 2⁶ = 721621357 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (721621427) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 360810710 + 360810711.

It is an arithmetic number, because the mean of its divisors is an integer number (360810711).

Almost surely, 2^721621421 is an apocalyptic number.

It is an amenable number.

721621421 is a deficient number, since it is larger than the sum of its proper divisors (1).

721621421 is an equidigital number, since it uses as much as digits as its factorization.

721621421 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1344, while the sum is 26.

The square root of 721621421 is about 26863.0121356485. The cubic root of 721621421 is about 896.9532452481.

Adding to 721621421 its reverse (124126127), we get a palindrome (845747548).

The spelling of 721621421 in words is "seven hundred twenty-one million, six hundred twenty-one thousand, four hundred twenty-one".