21997989 has 12 divisors (see below), whose sum is σ = 34219276. Its totient is φ = 13537152.

The previous prime is 21997981. The next prime is 21998027. The reversal of 21997989 is 98979912.

It can be written as a sum of positive squares in 2 ways, for example, as 7935489 + 14062500 = 2817^2 + 3750^2 .

It is not a de Polignac number, because 21997989 - 2³ = 21997981 is a prime.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21997981) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 93892 + ... + 94125.

Almost surely, 2^21997989 is an apocalyptic number.

It is an amenable number.

21997989 is a deficient number, since it is larger than the sum of its proper divisors (12221287).

21997989 is a wasteful number, since it uses less digits than its factorization.

21997989 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 188036 (or 188033 counting only the distinct ones).

The product of its digits is 734832, while the sum is 54.

The square root of 21997989 is about 4690.2013816040. The cubic root of 21997989 is about 280.1953950765.

It can be divided in two parts, 2 and 1997989, that added together give a palindrome (1997991).

The spelling of 21997989 in words is "twenty-one million, nine hundred ninety-seven thousand, nine hundred eighty-nine".