21639786 has 16 divisors (see below), whose sum is σ = 49462464. Its totient is φ = 6182784.

The previous prime is 21639773. The next prime is 21639791. The reversal of 21639786 is 68793612.

It is a happy number.

It is a Harshad number since it is a multiple of its sum of digits (42), and also a Moran number because the ratio is a prime number: 515233 = 21639786 / (2 + 1 + 6 + 3 + 9 + 7 + 8 + 6).

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 257575 + ... + 257658.

It is an arithmetic number, because the mean of its divisors is an integer number (3091404).

Almost surely, 2^21639786 is an apocalyptic number.

21639786 is an abundant number, since it is smaller than the sum of its proper divisors (27822678).

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

21639786 is a wasteful number, since it uses less digits than its factorization.

21639786 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 515245.

The product of its digits is 108864, while the sum is 42.

The square root of 21639786 is about 4651.8583383418. The cubic root of 21639786 is about 278.6662161141. Note that the first 3 decimals are identical.

The spelling of 21639786 in words is "twenty-one million, six hundred thirty-nine thousand, seven hundred eighty-six".