21521577 has 32 divisors (see below), whose sum is σ = 36071424. Its totient is φ = 11088000.

The previous prime is 21521557. The next prime is 21521579. The reversal of 21521577 is 77512512.

It is not a de Polignac number, because 21521577 - 2⁸ = 21521321 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21521579) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 34573 + ... + 35189.

It is an arithmetic number, because the mean of its divisors is an integer number (1127232).

Almost surely, 2^21521577 is an apocalyptic number.

It is an amenable number.

21521577 is a deficient number, since it is larger than the sum of its proper divisors (14549847).

21521577 is a wasteful number, since it uses less digits than its factorization.

21521577 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 789.

The product of its digits is 4900, while the sum is 30.

The square root of 21521577 is about 4639.1353720279. The cubic root of 21521577 is about 278.1578774751.

The spelling of 21521577 in words is "twenty-one million, five hundred twenty-one thousand, five hundred seventy-seven".