21087136 has 48 divisors (see below), whose sum is σ = 49521024. Its totient is φ = 8642304.

The previous prime is 21087133. The next prime is 21087137. The reversal of 21087136 is 63178012.

It is a Harshad number since it is a multiple of its sum of digits (28).

It is not an unprimeable number, because it can be changed into a prime (21087133) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 3106 + ... + 7198.

It is an arithmetic number, because the mean of its divisors is an integer number (1031688).

Almost surely, 2^21087136 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 21087136, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (24760512).

21087136 is an abundant number, since it is smaller than the sum of its proper divisors (28433888).

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

21087136 is a wasteful number, since it uses less digits than its factorization.

21087136 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4133 (or 4125 counting only the distinct ones).

The product of its (nonzero) digits is 2016, while the sum is 28.

The square root of 21087136 is about 4592.0731701488. The cubic root of 21087136 is about 276.2734809385.

It can be divided in two parts, 210871 and 36, that multiplied together give a triangular number (7591356 = T₃₈₉₆).

The spelling of 21087136 in words is "twenty-one million, eighty-seven thousand, one hundred thirty-six".