20643987 has 16 divisors (see below), whose sum is σ = 33877760. Its totient is φ = 10888992.

The previous prime is 20643947. The next prime is 20644003. The reversal of 20643987 is 78934602.

It is not a de Polignac number, because 20643987 - 2⁸ = 20643731 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (39).

It is not an unprimeable number, because it can be changed into a prime (20643907) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 37537 + ... + 38082.

It is an arithmetic number, because the mean of its divisors is an integer number (2117360).

Almost surely, 2^20643987 is an apocalyptic number.

20643987 is a deficient number, since it is larger than the sum of its proper divisors (13233773).

20643987 is a wasteful number, since it uses less digits than its factorization.

20643987 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 75642.

The product of its (nonzero) digits is 72576, while the sum is 39.

The square root of 20643987 is about 4543.5654501724. The cubic root of 20643987 is about 274.3244553646.

The spelling of 20643987 in words is "twenty million, six hundred forty-three thousand, nine hundred eighty-seven".