81721434037 has 2 divisors, whose sum is σ = 81721434038. Its totient is φ = 81721434036.

The previous prime is 81721434029. The next prime is 81721434049. The reversal of 81721434037 is 73043412718.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 41293897681 + 40427536356 = 203209^2 + 201066^2 .

It is a cyclic number.

It is not a de Polignac number, because 81721434037 - 2³ = 81721434029 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81721434097) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40860717018 + 40860717019.

It is an arithmetic number, because the mean of its divisors is an integer number (40860717019).

Almost surely, 2^81721434037 is an apocalyptic number.

It is an amenable number.

81721434037 is a deficient number, since it is larger than the sum of its proper divisors (1).

81721434037 is an equidigital number, since it uses as much as digits as its factorization.

81721434037 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 112896, while the sum is 40.

The spelling of 81721434037 in words is "eighty-one billion, seven hundred twenty-one million, four hundred thirty-four thousand, thirty-seven".