21157986 has 8 divisors (see below), whose sum is σ = 42315984. Its totient is φ = 7052660.

The previous prime is 21157973. The next prime is 21157987. The reversal of 21157986 is 68975112.

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

21157986 is an admirable number.

It is not an unprimeable number, because it can be changed into a prime (21157987) 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, 1763160 + ... + 1763171.

It is an arithmetic number, because the mean of its divisors is an integer number (5289498).

Almost surely, 2^21157986 is an apocalyptic number.

21157986 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.

21157986 is a wasteful number, since it uses less digits than its factorization.

21157986 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3526336.

The product of its digits is 30240, while the sum is 39.

The square root of 21157986 is about 4599.7810817473. The cubic root of 21157986 is about 276.5825492248.

It can be divided in two parts, 2115 and 7986, that added together give a palindrome (10101).

The spelling of 21157986 in words is "twenty-one million, one hundred fifty-seven thousand, nine hundred eighty-six".