21029978 has 8 divisors (see below), whose sum is σ = 31824468. Its totient is φ = 10421824.

The previous prime is 21029977. The next prime is 21030001. The reversal of 21029978 is 87992012.

It can be written as a sum of positive squares in 2 ways, for example, as 20912329 + 117649 = 4573^2 + 343^2 .

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 (21029971) 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, 46301 + ... + 46752.

Almost surely, 2^21029978 is an apocalyptic number.

21029978 is a deficient number, since it is larger than the sum of its proper divisors (10794490).

21029978 is a wasteful number, since it uses less digits than its factorization.

21029978 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 93168.

The product of its (nonzero) digits is 18144, while the sum is 38.

The square root of 21029978 is about 4585.8453964346. The cubic root of 21029978 is about 276.0236362170.

The spelling of 21029978 in words is "twenty-one million, twenty-nine thousand, nine hundred seventy-eight".