21277978 has 4 divisors (see below), whose sum is σ = 31916970. Its totient is φ = 10638988.

The previous prime is 21277969. The next prime is 21277979. The reversal of 21277978 is 87977212.

It is a happy number.

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., 21095649 + 182329 = 4593^2 + 427^2 .

It is not an unprimeable number, because it can be changed into a prime (21277979) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5319493 + ... + 5319496.

Almost surely, 2^21277978 is an apocalyptic number.

21277978 is a deficient number, since it is larger than the sum of its proper divisors (10638992).

21277978 is a wasteful number, since it uses less digits than its factorization.

21277978 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10638991.

The product of its digits is 98784, while the sum is 43.

The square root of 21277978 is about 4612.8058706171. The cubic root of 21277978 is about 277.1044191816.

The spelling of 21277978 in words is "twenty-one million, two hundred seventy-seven thousand, nine hundred seventy-eight".