21655978 has 8 divisors (see below), whose sum is σ = 32503968. Its totient is φ = 10821324.

The previous prime is 21655973. The next prime is 21655979. The reversal of 21655978 is 87955612.

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

It is not an unprimeable number, because it can be changed into a prime (21655973) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3675 + ... + 7537.

It is an arithmetic number, because the mean of its divisors is an integer number (4062996).

Almost surely, 2^21655978 is an apocalyptic number.

21655978 is a deficient number, since it is larger than the sum of its proper divisors (10847990).

21655978 is a wasteful number, since it uses less digits than its factorization.

21655978 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6668.

The product of its digits is 151200, while the sum is 43.

The square root of 21655978 is about 4653.5983926420. The cubic root of 21655978 is about 278.7357029138.

The spelling of 21655978 in words is "twenty-one million, six hundred fifty-five thousand, nine hundred seventy-eight".