20905421 has 4 divisors (see below), whose sum is σ = 20962752. Its totient is φ = 20848092.

The previous prime is 20905403. The next prime is 20905429. The reversal of 20905421 is 12450902.

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 20905421 - 2¹⁰ = 20904397 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20905429) 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, 28115 + ... + 28848.

It is an arithmetic number, because the mean of its divisors is an integer number (5240688).

Almost surely, 2^20905421 is an apocalyptic number.

It is an amenable number.

20905421 is a deficient number, since it is larger than the sum of its proper divisors (57331).

20905421 is an equidigital number, since it uses as much as digits as its factorization.

20905421 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 57330.

The product of its (nonzero) digits is 720, while the sum is 23.

The square root of 20905421 is about 4572.2446347500. The cubic root of 20905421 is about 275.4776096946.

The spelling of 20905421 in words is "twenty million, nine hundred five thousand, four hundred twenty-one".