21012500 has 54 divisors (see below), whose sum is σ = 47110266. Its totient is φ = 8200000.

The previous prime is 21012457. The next prime is 21012503. The reversal of 21012500 is 521012.

It is a powerful number, because all its prime factors have an exponent greater than 1 and also an Achilles number because it is not a perfect power.

It can be written as a sum of positive squares in 9 ways, for example, as 15713296 + 5299204 = 3964^2 + 2302^2 .

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21012503) by changing a digit.

It is a polite number, since it can be written in 17 ways as a sum of consecutive naturals, for example, 512480 + ... + 512520.

Almost surely, 2^21012500 is an apocalyptic number.

21012500 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 21012500, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (23555133).

21012500 is an abundant number, since it is smaller than the sum of its proper divisors (26097766).

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

21012500 is an frugal number, since it uses more digits than its factorization.

21012500 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 111 (or 48 counting only the distinct ones).

The product of its (nonzero) digits is 20, while the sum is 11.

The square root of 21012500 is about 4583.9393538746. The cubic root of 21012500 is about 275.9471473395.

Multiplying 21012500 by its product of nonzero digits (20), we get a square (420250000 = 20500²).

21012500 divided by its product of nonzero digits (20) gives a square (1050625 = 1025²).

Adding to 21012500 its reverse (521012), we get a palindrome (21533512).

It can be divided in two parts, 21012 and 500, that added together give a palindrome (21512).

The spelling of 21012500 in words is "twenty-one million, twelve thousand, five hundred".