21215987 has 16 divisors (see below), whose sum is σ = 23520000. Its totient is φ = 19017504.

The previous prime is 21215977. The next prime is 21215993. The reversal of 21215987 is 78951212.

It is a cyclic number.

It is not a de Polignac number, because 21215987 - 2¹² = 21211891 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21215977) 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, 106514 + ... + 106712.

It is an arithmetic number, because the mean of its divisors is an integer number (1470000).

Almost surely, 2^21215987 is an apocalyptic number.

21215987 is a deficient number, since it is larger than the sum of its proper divisors (2304013).

21215987 is a wasteful number, since it uses less digits than its factorization.

21215987 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 410.

The product of its digits is 10080, while the sum is 35.

The square root of 21215987 is about 4606.0815233775. The cubic root of 21215987 is about 276.8350532181.

The spelling of 21215987 in words is "twenty-one million, two hundred fifteen thousand, nine hundred eighty-seven".