21061638 has 24 divisors (see below), whose sum is σ = 49144368. Its totient is φ = 6480432.

The previous prime is 21061619. The next prime is 21061639. The reversal of 21061638 is 83616012.

21061638 is a `hidden beast` number, since 2 + 10 + 616 + 38 = 666.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21061639) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 44770 + ... + 45237.

It is an arithmetic number, because the mean of its divisors is an integer number (2047682).

Almost surely, 2^21061638 is an apocalyptic number.

21061638 is an abundant number, since it is smaller than the sum of its proper divisors (28082730).

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

21061638 is a wasteful number, since it uses less digits than its factorization.

21061638 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 90028 (or 90025 counting only the distinct ones).

The product of its (nonzero) digits is 1728, while the sum is 27.

The square root of 21061638 is about 4589.2960244465. The cubic root of 21061638 is about 276.1620818619.

The spelling of 21061638 in words is "twenty-one million, sixty-one thousand, six hundred thirty-eight".