21945978 has 20 divisors (see below), whose sum is σ = 49175610. Its totient is φ = 7315272.

The previous prime is 21945977. The next prime is 21946003. The reversal of 21945978 is 87954912.

It can be written as a sum of positive squares in only one way, i.e., 19686969 + 2259009 = 4437^2 + 1503^2 .

It is not an unprimeable number, because it can be changed into a prime (21945977) by changing a digit.

It is a polite number, since it can be written in 9 ways as a sum of consecutive naturals, for example, 67573 + ... + 67896.

Almost surely, 2^21945978 is an apocalyptic number.

21945978 is an abundant number, since it is smaller than the sum of its proper divisors (27229632).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21945978 is a wasteful number, since it uses less digits than its factorization.

21945978 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 135483 (or 135474 counting only the distinct ones).

The product of its digits is 181440, while the sum is 45.

The square root of 21945978 is about 4684.6534556998. The cubic root of 21945978 is about 279.9743939169.

The spelling of 21945978 in words is "twenty-one million, nine hundred forty-five thousand, nine hundred seventy-eight".