21658987 has 16 divisors (see below), whose sum is σ = 25759744. Its totient is φ = 17820000.

The previous prime is 21658979. The next prime is 21659017. The reversal of 21658987 is 78985612.

It is a cyclic number.

It is not a de Polignac number, because 21658987 - 2³ = 21658979 is a prime.

It is a super-2 number, since 2×21658987² = 938223435732338, which contains 22 as substring.

It is an alternating number because its digits alternate between even and odd.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21658937) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 32437 + ... + 33097.

It is an arithmetic number, because the mean of its divisors is an integer number (1609984).

Almost surely, 2^21658987 is an apocalyptic number.

21658987 is a deficient number, since it is larger than the sum of its proper divisors (4100757).

21658987 is a wasteful number, since it uses less digits than its factorization.

21658987 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 850.

The product of its digits is 241920, while the sum is 46.

The square root of 21658987 is about 4653.9216796160. The cubic root of 21658987 is about 278.7486120035.

The spelling of 21658987 in words is "twenty-one million, six hundred fifty-eight thousand, nine hundred eighty-seven".