21521819 has 4 divisors (see below), whose sum is σ = 23478360. Its totient is φ = 19565280.

The previous prime is 21521803. The next prime is 21521821. The reversal of 21521819 is 91812512.

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

It is a cyclic number.

It is not a de Polignac number, because 21521819 - 2⁴ = 21521803 is a prime.

It is a super-2 number, since 2×21521819² = 926377386137522, which contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21521791 and 21521800.

It is not an unprimeable number, because it can be changed into a prime (21521839) 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, 978254 + ... + 978275.

It is an arithmetic number, because the mean of its divisors is an integer number (5869590).

Almost surely, 2^21521819 is an apocalyptic number.

21521819 is a deficient number, since it is larger than the sum of its proper divisors (1956541).

21521819 is a wasteful number, since it uses less digits than its factorization.

21521819 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1956540.

The product of its digits is 1440, while the sum is 29.

The square root of 21521819 is about 4639.1614544010. The cubic root of 21521819 is about 278.1589200560.

The spelling of 21521819 in words is "twenty-one million, five hundred twenty-one thousand, eight hundred nineteen".