21399577 has 4 divisors (see below), whose sum is σ = 21611556. Its totient is φ = 21187600.

The previous prime is 21399563. The next prime is 21399649. The reversal of 21399577 is 77599312.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 14318656 + 7080921 = 3784^2 + 2661^2 .

It is a cyclic number.

It is not a de Polignac number, because 21399577 - 2¹⁵ = 21366809 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21399527) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 105838 + ... + 106039.

It is an arithmetic number, because the mean of its divisors is an integer number (5402889).

Almost surely, 2^21399577 is an apocalyptic number.

It is an amenable number.

21399577 is a deficient number, since it is larger than the sum of its proper divisors (211979).

21399577 is a wasteful number, since it uses less digits than its factorization.

21399577 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 211978.

The product of its digits is 119070, while the sum is 43.

The square root of 21399577 is about 4625.9676825503. The cubic root of 21399577 is about 277.6312805776.

The spelling of 21399577 in words is "twenty-one million, three hundred ninety-nine thousand, five hundred seventy-seven".