21506500 has 24 divisors (see below), whose sum is σ = 46971288. Its totient is φ = 8602400.

The previous prime is 21506491. The next prime is 21506519. The reversal of 21506500 is 560512.

It is a happy number.

It can be written as a sum of positive squares in 4 ways, for example, as 51076 + 21455424 = 226^2 + 4632^2 .

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 21007 + ... + 22006.

It is an arithmetic number, because the mean of its divisors is an integer number (1957137).

Almost surely, 2^21506500 is an apocalyptic number.

21506500 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21506500 is an abundant number, since it is smaller than the sum of its proper divisors (25464788).

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

21506500 is a wasteful number, since it uses less digits than its factorization.

21506500 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 43032 (or 43020 counting only the distinct ones).

The product of its (nonzero) digits is 300, while the sum is 19.

The square root of 21506500 is about 4637.5101078057. The cubic root of 21506500 is about 278.0929075456.

It can be divided in two parts, 21 and 506500, that added together give a triangular number (506521 = T₁₀₀₆).

The spelling of 21506500 in words is "twenty-one million, five hundred six thousand, five hundred".