21993687 has 24 divisors (see below), whose sum is σ = 34092240. Its totient is φ = 14152320.

The previous prime is 21993677. The next prime is 21993691. The reversal of 21993687 is 78639912.

It is not a de Polignac number, because 21993687 - 2²³ = 13605079 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21993637) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 5487 + ... + 8607.

It is an arithmetic number, because the mean of its divisors is an integer number (1420510).

Almost surely, 2^21993687 is an apocalyptic number.

21993687 is a gapful number since it is divisible by the number (27) formed by its first and last digit.

21993687 is a deficient number, since it is larger than the sum of its proper divisors (12098553).

21993687 is an equidigital number, since it uses as much as digits as its factorization.

21993687 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3165 (or 3153 counting only the distinct ones).

The product of its digits is 163296, while the sum is 45.

The square root of 21993687 is about 4689.7427434775. The cubic root of 21993687 is about 280.1771285707.

It can be divided in two parts, 2199 and 3687, that added together give a triangular number (5886 = T₁₀₈).

The spelling of 21993687 in words is "twenty-one million, nine hundred ninety-three thousand, six hundred eighty-seven".