21005678 has 16 divisors (see below), whose sum is σ = 33261840. Its totient is φ = 9921600.

The previous prime is 21005669. The next prime is 21005681. The reversal of 21005678 is 87650012.

It is a self number, because there is not a number n which added to its sum of digits gives 21005678.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 19268 + ... + 20328.

It is an arithmetic number, because the mean of its divisors is an integer number (2078865).

Almost surely, 2^21005678 is an apocalyptic number.

21005678 is a deficient number, since it is larger than the sum of its proper divisors (12256162).

21005678 is a wasteful number, since it uses less digits than its factorization.

21005678 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1603.

The product of its (nonzero) digits is 3360, while the sum is 29.

The square root of 21005678 is about 4583.1951736752. The cubic root of 21005678 is about 275.9172807490.

The spelling of 21005678 in words is "twenty-one million, five thousand, six hundred seventy-eight".