81972746021 has 2 divisors, whose sum is σ = 81972746022. Its totient is φ = 81972746020.

The previous prime is 81972745963. The next prime is 81972746069. The reversal of 81972746021 is 12064727918.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 61298332225 + 20674413796 = 247585^2 + 143786^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-81972746021 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81972746081) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40986373010 + 40986373011.

It is an arithmetic number, because the mean of its divisors is an integer number (40986373011).

Almost surely, 2^81972746021 is an apocalyptic number.

It is an amenable number.

81972746021 is a deficient number, since it is larger than the sum of its proper divisors (1).

81972746021 is an equidigital number, since it uses as much as digits as its factorization.

81972746021 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 338688, while the sum is 47.

The spelling of 81972746021 in words is "eighty-one billion, nine hundred seventy-two million, seven hundred forty-six thousand, twenty-one".