21997986 has 8 divisors (see below), whose sum is σ = 43995984. Its totient is φ = 7332660.

The previous prime is 21997981. The next prime is 21998027. The reversal of 21997986 is 68979912.

It is a happy number.

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

21997986 is an admirable number.

It is a super-2 number, since 2×21997986² = 967822776112392, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21997981) 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 3 ways as a sum of consecutive naturals, for example, 1833160 + ... + 1833171.

It is an arithmetic number, because the mean of its divisors is an integer number (5499498).

Almost surely, 2^21997986 is an apocalyptic number.

21997986 is a primitive abundant number, since it is smaller than the sum of its proper divisors, none of which is abundant.

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21997986 is a wasteful number, since it uses less digits than its factorization.

21997986 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3666336.

The product of its digits is 489888, while the sum is 51.

The square root of 21997986 is about 4690.2010617883. The cubic root of 21997986 is about 280.1953823391.

The spelling of 21997986 in words is "twenty-one million, nine hundred ninety-seven thousand, nine hundred eighty-six".