21042399778 has 4 divisors (see below), whose sum is σ = 31563599670. Its totient is φ = 10521199888.

The previous prime is 21042399727. The next prime is 21042399799. The reversal of 21042399778 is 87799324012.

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., 20739744169 + 302655609 = 144013^2 + 17397^2 .

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5260599943 + ... + 5260599946.

Almost surely, 2^21042399778 is an apocalyptic number.

21042399778 is a deficient number, since it is larger than the sum of its proper divisors (10521199892).

21042399778 is a wasteful number, since it uses less digits than its factorization.

21042399778 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10521199891.

The product of its (nonzero) digits is 1524096, while the sum is 52.

The spelling of 21042399778 in words is "twenty-one billion, forty-two million, three hundred ninety-nine thousand, seven hundred seventy-eight".