21988693 has 8 divisors (see below), whose sum is σ = 23011128. Its totient is φ = 20988864.

The previous prime is 21988657. The next prime is 21988697. The reversal of 21988693 is 39688912.

It can be written as a sum of positive squares in 4 ways, for example, as 4028049 + 17960644 = 2007^2 + 4238^2 .

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

It is a cyclic number.

It is not a de Polignac number, because 21988693 - 2¹⁷ = 21857621 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21988697) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 3646 + ... + 7567.

It is an arithmetic number, because the mean of its divisors is an integer number (2876391).

Almost surely, 2^21988693 is an apocalyptic number.

It is an amenable number.

21988693 is a deficient number, since it is larger than the sum of its proper divisors (1022435).

21988693 is a wasteful number, since it uses less digits than its factorization.

21988693 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 11303.

The product of its digits is 186624, while the sum is 46.

The square root of 21988693 is about 4689.2102746625. The cubic root of 21988693 is about 280.1559208109.

The spelling of 21988693 in words is "twenty-one million, nine hundred eighty-eight thousand, six hundred ninety-three".