21287772 has 108 divisors (see below), whose sum is σ = 61676888. Its totient is φ = 6415200.

The previous prime is 21287767. The next prime is 21287797. The reversal of 21287772 is 27778212.

It is a tau number, because it is divible by the number of its divisors (108).

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 35 ways as a sum of consecutive naturals, for example, 117522 + ... + 117702.

Almost surely, 2^21287772 is an apocalyptic number.

21287772 is a gapful number since it is divisible by the number (22) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21287772, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (30838444).

21287772 is an abundant number, since it is smaller than the sum of its proper divisors (40389116).

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

21287772 is a wasteful number, since it uses less digits than its factorization.

21287772 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 222 (or 197 counting only the distinct ones).

The product of its digits is 21952, while the sum is 36.

The square root of 21287772 is about 4613.8673583015. The cubic root of 21287772 is about 277.1469286154.

The spelling of 21287772 in words is "twenty-one million, two hundred eighty-seven thousand, seven hundred seventy-two".