21015900 has 108 divisors (see below), whose sum is σ = 69396600. Its totient is φ = 5304960.

The previous prime is 21015871. The next prime is 21015913. The reversal of 21015900 is 951012.

It is a Harshad number since it is a multiple of its sum of digits (18).

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 35 ways as a sum of consecutive naturals, for example, 16486 + ... + 17714.

Almost surely, 2^21015900 is an apocalyptic number.

21015900 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 21015900, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (34698300).

21015900 is an abundant number, since it is smaller than the sum of its proper divisors (48380700).

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

21015900 is a wasteful number, since it uses less digits than its factorization.

21015900 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1268 (or 1258 counting only the distinct ones).

The product of its (nonzero) digits is 90, while the sum is 18.

The square root of 21015900 is about 4584.3101989285. The cubic root of 21015900 is about 275.9620300633.

Adding to 21015900 its reverse (951012), we get a palindrome (21966912).

It can be divided in two parts, 2101 and 5900, that added together give a triangular number (8001 = T₁₂₆).

The spelling of 21015900 in words is "twenty-one million, fifteen thousand, nine hundred".