21397778 has 8 divisors (see below), whose sum is σ = 32119500. Its totient is φ = 10691280.

The previous prime is 21397771. The next prime is 21397787. The reversal of 21397778 is 87779312.

It can be written as a sum of positive squares in 2 ways, for example, as 12439729 + 8958049 = 3527^2 + 2993^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is not an unprimeable number, because it can be changed into a prime (21397771) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 848 + ... + 6596.

Almost surely, 2^21397778 is an apocalyptic number.

21397778 is a deficient number, since it is larger than the sum of its proper divisors (10721722).

21397778 is a wasteful number, since it uses less digits than its factorization.

21397778 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7612.

The product of its digits is 148176, while the sum is 44.

The square root of 21397778 is about 4625.7732326607. The cubic root of 21397778 is about 277.6235004757.

The spelling of 21397778 in words is "twenty-one million, three hundred ninety-seven thousand, seven hundred seventy-eight".