21987810 has 48 divisors (see below), whose sum is σ = 61569144. Its totient is φ = 5412096.

The previous prime is 21987809. The next prime is 21987821. The reversal of 21987810 is 1878912.

It can be written as a sum of positive squares in 4 ways, for example, as 16184529 + 5803281 = 4023^2 + 2409^2 .

It is a super-2 number, since 2×21987810² = 966927577192200, which contains 22 as substring.

It is a Curzon number.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 8227 + ... + 10566.

Almost surely, 2^21987810 is an apocalyptic number.

21987810 is an abundant number, since it is smaller than the sum of its proper divisors (39581334).

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

21987810 is a wasteful number, since it uses less digits than its factorization.

21987810 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 18819 (or 18816 counting only the distinct ones).

The product of its (nonzero) digits is 8064, while the sum is 36.

The square root of 21987810 is about 4689.1161214028. The cubic root of 21987810 is about 280.1521706867.

The spelling of 21987810 in words is "twenty-one million, nine hundred eighty-seven thousand, eight hundred ten".