721381 has 2 divisors, whose sum is σ = 721382. Its totient is φ = 721380.

The previous prime is 721379. The next prime is 721387. The reversal of 721381 is 183127.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 372100 + 349281 = 610^2 + 591^2 .

It is a cyclic number.

It is not a de Polignac number, because 721381 - 2¹ = 721379 is a prime.

It is a super-2 number, since 2×721381² = 1040781094322, which contains 22 as substring.

Together with 721379, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (721387) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 360690 + 360691.

It is an arithmetic number, because the mean of its divisors is an integer number (360691).

2⁷²¹³⁸¹ is an apocalyptic number.

It is an amenable number.

721381 is a deficient number, since it is larger than the sum of its proper divisors (1).

721381 is an equidigital number, since it uses as much as digits as its factorization.

721381 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 336, while the sum is 22.

The square root of 721381 is about 849.3415096414. The cubic root of 721381 is about 89.6853622213.

The spelling of 721381 in words is "seven hundred twenty-one thousand, three hundred eighty-one".