21978994 has 16 divisors (see below), whose sum is σ = 35569368. Its totient is φ = 10147072.

The previous prime is 21978989. The next prime is 21978997. The reversal of 21978994 is 49987912.

It can be written as a sum of positive squares in 4 ways, for example, as 21967969 + 11025 = 4687^2 + 105^2 .

It is not an unprimeable number, because it can be changed into a prime (21978997) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 4297 + ... + 7900.

Almost surely, 2^21978994 is an apocalyptic number.

21978994 is a deficient number, since it is larger than the sum of its proper divisors (13590374).

21978994 is a wasteful number, since it uses less digits than its factorization.

21978994 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 12269.

The product of its digits is 326592, while the sum is 49.

The square root of 21978994 is about 4688.1759779257. The cubic root of 21978994 is about 280.1147233965.

The spelling of 21978994 in words is "twenty-one million, nine hundred seventy-eight thousand, nine hundred ninety-four".