21505621 has 12 divisors (see below), whose sum is σ = 23097312. Its totient is φ = 19985328.

The previous prime is 21505543. The next prime is 21505637. The reversal of 21505621 is 12650512.

It is not a de Polignac number, because 21505621 - 2⁹ = 21505109 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21505592 and 21505601.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21505681) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 31146 + ... + 31828.

It is an arithmetic number, because the mean of its divisors is an integer number (1924776).

Almost surely, 2^21505621 is an apocalyptic number.

It is an amenable number.

21505621 is a deficient number, since it is larger than the sum of its proper divisors (1591691).

21505621 is an equidigital number, since it uses as much as digits as its factorization.

21505621 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 780 (or 743 counting only the distinct ones).

The product of its (nonzero) digits is 600, while the sum is 22.

The square root of 21505621 is about 4637.4153361544. The cubic root of 21505621 is about 278.0891188151.

The spelling of 21505621 in words is "twenty-one million, five hundred five thousand, six hundred twenty-one".