21661610 has 8 divisors (see below), whose sum is σ = 38990916. Its totient is φ = 8664640.

The previous prime is 21661609. The next prime is 21661639. The reversal of 21661610 is 1616612.

It can be written as a sum of positive squares in 2 ways, for example, as 21003889 + 657721 = 4583^2 + 811^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a Curzon number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1083071 + ... + 1083090.

Almost surely, 2^21661610 is an apocalyptic number.

21661610 is a deficient number, since it is larger than the sum of its proper divisors (17329306).

21661610 is a wasteful number, since it uses less digits than its factorization.

21661610 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2166168.

The product of its (nonzero) digits is 432, while the sum is 23.

The square root of 21661610 is about 4654.2034764286. The cubic root of 21661610 is about 278.7598641163.

The spelling of 21661610 in words is "twenty-one million, six hundred sixty-one thousand, six hundred ten".