21061500 has 96 divisors (see below), whose sum is σ = 64646400. Its totient is φ = 5313600.

The previous prime is 21061477. The next prime is 21061507. The reversal of 21061500 is 516012.

It is a Harshad number since it is a multiple of its sum of digits (15).

It is a self number, because there is not a number n which added to its sum of digits gives 21061500.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21061507) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 28131 + ... + 28869.

It is an arithmetic number, because the mean of its divisors is an integer number (673400).

Almost surely, 2^21061500 is an apocalyptic number.

21061500 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 21061500, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32323200).

21061500 is an abundant number, since it is smaller than the sum of its proper divisors (43584900).

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

21061500 is a wasteful number, since it uses less digits than its factorization.

21061500 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 780 (or 768 counting only the distinct ones).

The product of its (nonzero) digits is 60, while the sum is 15.

The square root of 21061500 is about 4589.2809894361. The cubic root of 21061500 is about 276.1614787045.

Adding to 21061500 its reverse (516012), we get a palindrome (21577512).

The spelling of 21061500 in words is "twenty-one million, sixty-one thousand, five hundred".