21678021 has 12 divisors (see below), whose sum is σ = 32323200. Its totient is φ = 13985640.

The previous prime is 21678001. The next prime is 21678037. The reversal of 21678021 is 12087612.

It is not a de Polignac number, because 21678021 - 2⁵ = 21677989 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21678001) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 38571 + ... + 39128.

It is an arithmetic number, because the mean of its divisors is an integer number (2693600).

Almost surely, 2^21678021 is an apocalyptic number.

It is an amenable number.

21678021 is a deficient number, since it is larger than the sum of its proper divisors (10645179).

21678021 is a wasteful number, since it uses less digits than its factorization.

21678021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 77736 (or 77733 counting only the distinct ones).

The product of its (nonzero) digits is 1344, while the sum is 27.

The square root of 21678021 is about 4655.9661725575. The cubic root of 21678021 is about 278.8302432084.

The spelling of 21678021 in words is "twenty-one million, six hundred seventy-eight thousand, twenty-one".