20421587 has 4 divisors (see below), whose sum is σ = 20447640. Its totient is φ = 20395536.

The previous prime is 20421571. The next prime is 20421593. The reversal of 20421587 is 78512402.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 78512402 = 2 ⋅39256201.

It is a cyclic number.

It is not a de Polignac number, because 20421587 - 2⁴ = 20421571 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20421187) 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, 11813 + ... + 13430.

It is an arithmetic number, because the mean of its divisors is an integer number (5111910).

Almost surely, 2^20421587 is an apocalyptic number.

20421587 is a deficient number, since it is larger than the sum of its proper divisors (26053).

20421587 is an equidigital number, since it uses as much as digits as its factorization.

20421587 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 26052.

The product of its (nonzero) digits is 4480, while the sum is 29.

The square root of 20421587 is about 4519.0250054630. The cubic root of 20421587 is about 273.3357870426.

Adding to 20421587 its reverse (78512402), we get a palindrome (98933989).

The spelling of 20421587 in words is "twenty million, four hundred twenty-one thousand, five hundred eighty-seven".