21997978326 has 16 divisors (see below), whose sum is σ = 48884396400. Its totient is φ = 7332659424.

The previous prime is 21997978309. The next prime is 21997978339. The reversal of 21997978326 is 62387979912.

21997978326 is a `hidden beast` number, since 219 + 9 + 7 + 97 + 8 + 326 = 666.

It is a super-2 number, since 2×21997978326² (a number of 21 digits) contains 22 as substring.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 203684931 + ... + 203685038.

It is an arithmetic number, because the mean of its divisors is an integer number (3055274775).

Almost surely, 2^21997978326 is an apocalyptic number.

21997978326 is an abundant number, since it is smaller than the sum of its proper divisors (26886418074).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21997978326 is a wasteful number, since it uses less digits than its factorization.

21997978326 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 407369980 (or 407369974 counting only the distinct ones).

The product of its digits is 20575296, while the sum is 63.

The spelling of 21997978326 in words is "twenty-one billion, nine hundred ninety-seven million, nine hundred seventy-eight thousand, three hundred twenty-six".