21640767994 has 4 divisors (see below), whose sum is σ = 32461151994. Its totient is φ = 10820383996.

The previous prime is 21640767983. The next prime is 21640768027. The reversal of 21640767994 is 49976704612.

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., 21108312369 + 532455625 = 145287^2 + 23075^2 .

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5410191997 + ... + 5410192000.

Almost surely, 2^21640767994 is an apocalyptic number.

21640767994 is a deficient number, since it is larger than the sum of its proper divisors (10820384000).

21640767994 is a wasteful number, since it uses less digits than its factorization.

21640767994 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10820383999.

The product of its (nonzero) digits is 4572288, while the sum is 55.

The spelling of 21640767994 in words is "twenty-one billion, six hundred forty million, seven hundred sixty-seven thousand, nine hundred ninety-four".