21661678 has 8 divisors (see below), whose sum is σ = 32529672. Its totient is φ = 10818456.

The previous prime is 21661657. The next prime is 21661681. The reversal of 21661678 is 87616612.

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

It is a congruent 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, 3825 + ... + 7612.

It is an arithmetic number, because the mean of its divisors is an integer number (4066209).

Almost surely, 2^21661678 is an apocalyptic number.

21661678 is a deficient number, since it is larger than the sum of its proper divisors (10867994).

21661678 is a wasteful number, since it uses less digits than its factorization.

21661678 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 12386.

The product of its digits is 24192, while the sum is 37.

The square root of 21661678 is about 4654.2107816471. The cubic root of 21661678 is about 278.7601558098.

It can be divided in two parts, 2166 and 1678, that added together give a square (3844 = 62²).

The spelling of 21661678 in words is "twenty-one million, six hundred sixty-one thousand, six hundred seventy-eight".