21640386 has 8 divisors (see below), whose sum is σ = 43280784. Its totient is φ = 7213460.

The previous prime is 21640379. The next prime is 21640427. The reversal of 21640386 is 68304612.

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

21640386 is an admirable number.

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, 1803360 + ... + 1803371.

It is an arithmetic number, because the mean of its divisors is an integer number (5410098).

Almost surely, 2^21640386 is an apocalyptic number.

21640386 is a primitive abundant number, since it is smaller than the sum of its proper divisors, none of which is abundant.

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

21640386 is a wasteful number, since it uses less digits than its factorization.

21640386 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3606736.

The product of its (nonzero) digits is 6912, while the sum is 30.

The square root of 21640386 is about 4651.9228282507. The cubic root of 21640386 is about 278.6687915891.

Adding to 21640386 its reverse (68304612), we get a palindrome (89944998).

The spelling of 21640386 in words is "twenty-one million, six hundred forty thousand, three hundred eighty-six".