21801972194 has 4 divisors (see below), whose sum is σ = 32702958294. Its totient is φ = 10900986096.

The previous prime is 21801972163. The next prime is 21801972217. The reversal of 21801972194 is 49127910812.

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., 15206095969 + 6595876225 = 123313^2 + 81215^2 .

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5450493047 + ... + 5450493050.

Almost surely, 2^21801972194 is an apocalyptic number.

21801972194 is a deficient number, since it is larger than the sum of its proper divisors (10900986100).

21801972194 is a wasteful number, since it uses less digits than its factorization.

21801972194 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10900986099.

The product of its (nonzero) digits is 72576, while the sum is 44.

The spelling of 21801972194 in words is "twenty-one billion, eight hundred one million, nine hundred seventy-two thousand, one hundred ninety-four".