21516840 has 160 divisors (see below), whose sum is σ = 75141000. Its totient is φ = 5515776.

The previous prime is 21516829. The next prime is 21516853. The reversal of 21516840 is 4861512.

It can be written as a sum of positive squares in 4 ways, for example, as 20738916 + 777924 = 4554^2 + 882^2 .

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

It is an unprimeable number.

It is a polite number, since it can be written in 39 ways as a sum of consecutive naturals, for example, 93846 + ... + 94074.

Almost surely, 2^21516840 is an apocalyptic number.

21516840 is a gapful number since it is divisible by the number (20) 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 21516840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (37570500).

21516840 is an abundant number, since it is smaller than the sum of its proper divisors (53624160).

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

21516840 is a wasteful number, since it uses less digits than its factorization.

21516840 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 281 (or 268 counting only the distinct ones).

The product of its (nonzero) digits is 1920, while the sum is 27.

The square root of 21516840 is about 4638.6247962085. The cubic root of 21516840 is about 278.1374680267.

The spelling of 21516840 in words is "twenty-one million, five hundred sixteen thousand, eight hundred forty".