21185661 has 16 divisors (see below), whose sum is σ = 32832000. Its totient is φ = 11900208.

The previous prime is 21185657. The next prime is 21185687. The reversal of 21185661 is 16658112.

It is not a de Polignac number, because 21185661 - 2² = 21185657 is a prime.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21185641) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 7311 + ... + 9788.

It is an arithmetic number, because the mean of its divisors is an integer number (2052000).

Almost surely, 2^21185661 is an apocalyptic number.

21185661 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

21185661 is a deficient number, since it is larger than the sum of its proper divisors (11646339).

21185661 is a wasteful number, since it uses less digits than its factorization.

21185661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 17168.

The product of its digits is 2880, while the sum is 30.

The square root of 21185661 is about 4602.7883940064. The cubic root of 21185661 is about 276.7030882197.

The spelling of 21185661 in words is "twenty-one million, one hundred eighty-five thousand, six hundred sixty-one".