21505700 has 36 divisors (see below), whose sum is σ = 47119380. Its totient is φ = 8519040.

The previous prime is 21505699. The next prime is 21505709. The reversal of 21505700 is 750512.

It can be written as a sum of positive squares in 6 ways, for example, as 784996 + 20720704 = 886^2 + 4552^2 .

It is a Harshad number since it is a multiple of its sum of digits (20).

It is not an unprimeable number, because it can be changed into a prime (21505709) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 9914 + ... + 11886.

Almost surely, 2^21505700 is an apocalyptic number.

21505700 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 21505700, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (23559690).

21505700 is an abundant number, since it is smaller than the sum of its proper divisors (25613680).

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

21505700 is a wasteful number, since it uses less digits than its factorization.

21505700 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2096 (or 2089 counting only the distinct ones).

The product of its (nonzero) digits is 350, while the sum is 20.

The square root of 21505700 is about 4637.4238538223. The cubic root of 21505700 is about 278.0894593310.

The spelling of 21505700 in words is "twenty-one million, five hundred five thousand, seven hundred".