21173621 has 4 divisors (see below), whose sum is σ = 24198432. Its totient is φ = 18148812.

The previous prime is 21173611. The next prime is 21173623. The reversal of 21173621 is 12637112.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21173621 - 2¹⁸ = 20911477 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21173623) 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, 1512395 + ... + 1512408.

It is an arithmetic number, because the mean of its divisors is an integer number (6049608).

Almost surely, 2^21173621 is an apocalyptic number.

It is an amenable number.

21173621 is a deficient number, since it is larger than the sum of its proper divisors (3024811).

21173621 is an equidigital number, since it uses as much as digits as its factorization.

21173621 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3024810.

The product of its digits is 504, while the sum is 23.

The square root of 21173621 is about 4601.4803052931. The cubic root of 21173621 is about 276.6506606763.

The spelling of 21173621 in words is "twenty-one million, one hundred seventy-three thousand, six hundred twenty-one".