21077978 has 4 divisors (see below), whose sum is σ = 31616970. Its totient is φ = 10538988.

The previous prime is 21077971. The next prime is 21078053. The reversal of 21077978 is 87977012.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in only one way, i.e., 20912329 + 165649 = 4573^2 + 407^2 .

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21077971) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5269493 + ... + 5269496.

Almost surely, 2^21077978 is an apocalyptic number.

21077978 is a deficient number, since it is larger than the sum of its proper divisors (10538992).

21077978 is a wasteful number, since it uses less digits than its factorization.

21077978 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10538991.

The product of its (nonzero) digits is 49392, while the sum is 41.

The square root of 21077978 is about 4591.0759087604. The cubic root of 21077978 is about 276.2334805816.

The spelling of 21077978 in words is "twenty-one million, seventy-seven thousand, nine hundred seventy-eight".