21531636 has 96 divisors (see below), whose sum is σ = 67200000. Its totient is φ = 5824224.

The previous prime is 21531623. The next prime is 21531641. The reversal of 21531636 is 63613512.

21531636 is a `hidden beast` number, since 21 + 5 + 3 + 1 + 636 = 666.

It is a super-2 number, since 2×21531636² = 927222697672992, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (27).

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, 13615 + ... + 15113.

It is an arithmetic number, because the mean of its divisors is an integer number (700000).

Almost surely, 2^21531636 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 21531636, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (33600000).

21531636 is an abundant number, since it is smaller than the sum of its proper divisors (45668364).

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

21531636 is a wasteful number, since it uses less digits than its factorization.

21531636 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1538 (or 1530 counting only the distinct ones).

The product of its digits is 3240, while the sum is 27.

The square root of 21531636 is about 4640.2193913650. The cubic root of 21531636 is about 278.2012069251.

The spelling of 21531636 in words is "twenty-one million, five hundred thirty-one thousand, six hundred thirty-six".