721421521 has 2 divisors, whose sum is σ = 721421522. Its totient is φ = 721421520.

The previous prime is 721421461. The next prime is 721421539. The reversal of 721421521 is 125124127.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 684345600 + 37075921 = 26160^2 + 6089^2 .

It is a cyclic number.

It is not a de Polignac number, because 721421521 - 2⁹ = 721421009 is a prime.

It is not a weakly prime, because it can be changed into another prime (721421021) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 360710760 + 360710761.

It is an arithmetic number, because the mean of its divisors is an integer number (360710761).

Almost surely, 2^721421521 is an apocalyptic number.

It is an amenable number.

721421521 is a deficient number, since it is larger than the sum of its proper divisors (1).

721421521 is an equidigital number, since it uses as much as digits as its factorization.

721421521 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1120, while the sum is 25.

The square root of 721421521 is about 26859.2911485020. The cubic root of 721421521 is about 896.8704144140.

Adding to 721421521 its reverse (125124127), we get a palindrome (846545648).

The spelling of 721421521 in words is "seven hundred twenty-one million, four hundred twenty-one thousand, five hundred twenty-one".