21636989 has 4 divisors (see below), whose sum is σ = 23604000. Its totient is φ = 19669980.

The previous prime is 21636961. The next prime is 21637009. The reversal of 21636989 is 98963612.

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 not a de Polignac number, because 21636989 - 2²⁰ = 20588413 is a prime.

It is a super-2 number, since 2×21636989² = 936318585972242, which contains 22 as substring.

It is an alternating number because its digits alternate between even and odd.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21636919) 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, 983489 + ... + 983510.

It is an arithmetic number, because the mean of its divisors is an integer number (5901000).

Almost surely, 2^21636989 is an apocalyptic number.

It is an amenable number.

21636989 is a deficient number, since it is larger than the sum of its proper divisors (1967011).

21636989 is a wasteful number, since it uses less digits than its factorization.

21636989 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1967010.

The product of its digits is 139968, while the sum is 44.

The square root of 21636989 is about 4651.5576960842. The cubic root of 21636989 is about 278.6542094798.

The spelling of 21636989 in words is "twenty-one million, six hundred thirty-six thousand, nine hundred eighty-nine".