21991284 has 96 divisors (see below), whose sum is σ = 68633600. Its totient is φ = 5948640.

The previous prime is 21991279. The next prime is 21991301. The reversal of 21991284 is 48219912.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 13599 + ... + 15129.

Almost surely, 2^21991284 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21991284, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (34316800).

21991284 is an abundant number, since it is smaller than the sum of its proper divisors (46642316).

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

21991284 is a wasteful number, since it uses less digits than its factorization.

21991284 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1570 (or 1562 counting only the distinct ones).

The product of its digits is 10368, while the sum is 36.

The square root of 21991284 is about 4689.4865390573. The cubic root of 21991284 is about 280.1669242765.

The spelling of 21991284 in words is "twenty-one million, nine hundred ninety-one thousand, two hundred eighty-four".