20421561 has 8 divisors (see below), whose sum is σ = 28661920. Its totient is φ = 12897792.

The previous prime is 20421553. The next prime is 20421571. The reversal of 20421561 is 16512402.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 20421561 - 2³ = 20421553 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20421571) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 179080 + ... + 179193.

It is an arithmetic number, because the mean of its divisors is an integer number (3582740).

Almost surely, 2^20421561 is an apocalyptic number.

It is an amenable number.

20421561 is a deficient number, since it is larger than the sum of its proper divisors (8240359).

20421561 is a wasteful number, since it uses less digits than its factorization.

20421561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 358295.

The product of its (nonzero) digits is 480, while the sum is 21.

The square root of 20421561 is about 4519.0221287354. The cubic root of 20421561 is about 273.3356710422.

Adding to 20421561 its reverse (16512402), we get a palindrome (36933963).

The spelling of 20421561 in words is "twenty million, four hundred twenty-one thousand, five hundred sixty-one".