21861520 has 20 divisors (see below), whose sum is σ = 50828220. Its totient is φ = 8744576.

The previous prime is 21861517. The next prime is 21861547. The reversal of 21861520 is 2516812.

It can be written as a sum of positive squares in 2 ways, for example, as 9834496 + 12027024 = 3136^2 + 3468^2 .

It is a tau number, because it is divible by the number of its divisors (20).

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 136555 + ... + 136714.

It is an arithmetic number, because the mean of its divisors is an integer number (2541411).

Almost surely, 2^21861520 is an apocalyptic number.

21861520 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21861520 is an abundant number, since it is smaller than the sum of its proper divisors (28966700).

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

21861520 is a wasteful number, since it uses less digits than its factorization.

21861520 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 273282 (or 273276 counting only the distinct ones).

The product of its (nonzero) digits is 960, while the sum is 25.

The square root of 21861520 is about 4675.6304387751. The cubic root of 21861520 is about 279.6147763754.

The spelling of 21861520 in words is "twenty-one million, eight hundred sixty-one thousand, five hundred twenty".