21981962817 has 10 divisors (see below), whose sum is σ = 32837253218. Its totient is φ = 14654641824.

The previous prime is 21981962813. The next prime is 21981962869. The reversal of 21981962817 is 71826918912.

It is a happy number.

21981962817 is a `hidden beast` number, since 2 + 1 + 9 + 8 + 1 + 9 + 628 + 1 + 7 = 666.

It can be written as a sum of positive squares in only one way, i.e., 13155172416 + 8826790401 = 114696^2 + 93951^2 .

It is not a de Polignac number, because 21981962817 - 2² = 21981962813 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21981962813) by changing a digit.

It is a polite number, since it can be written in 9 ways as a sum of consecutive naturals, for example, 135691048 + ... + 135691209.

Almost surely, 2^21981962817 is an apocalyptic number.

21981962817 is a gapful number since it is divisible by the number (27) formed by its first and last digit.

It is an amenable number.

21981962817 is a deficient number, since it is larger than the sum of its proper divisors (10855290401).

21981962817 is an equidigital number, since it uses as much as digits as its factorization.

21981962817 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 271382269 (or 271382260 counting only the distinct ones).

The product of its digits is 870912, while the sum is 54.

The spelling of 21981962817 in words is "twenty-one billion, nine hundred eighty-one million, nine hundred sixty-two thousand, eight hundred seventeen".