20997863818 has 4 divisors (see below), whose sum is σ = 31496795730. Its totient is φ = 10498931908.

The previous prime is 20997863797. The next prime is 20997863833. The reversal of 20997863818 is 81836879902.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 81836879902 = 2 ⋅40918439951.

It can be written as a sum of positive squares in only one way, i.e., 11149881649 + 9847982169 = 105593^2 + 99237^2 .

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5249465953 + ... + 5249465956.

Almost surely, 2^20997863818 is an apocalyptic number.

20997863818 is a deficient number, since it is larger than the sum of its proper divisors (10498931912).

20997863818 is a wasteful number, since it uses less digits than its factorization.

20997863818 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10498931911.

The product of its (nonzero) digits is 10450944, while the sum is 61.

The spelling of 20997863818 in words is "twenty billion, nine hundred ninety-seven million, eight hundred sixty-three thousand, eight hundred eighteen".