81723621437 has 4 divisors (see below), whose sum is σ = 81735974880. Its totient is φ = 81711267996.

The previous prime is 81723621409. The next prime is 81723621451. The reversal of 81723621437 is 73412632718.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 81723621437 - 2²⁴ = 81706844221 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81723627437) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 6166793 + ... + 6180030.

It is an arithmetic number, because the mean of its divisors is an integer number (20433993720).

Almost surely, 2^81723621437 is an apocalyptic number.

It is an amenable number.

81723621437 is a deficient number, since it is larger than the sum of its proper divisors (12353443).

81723621437 is a wasteful number, since it uses less digits than its factorization.

81723621437 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 12353442.

The product of its digits is 338688, while the sum is 44.

The spelling of 81723621437 in words is "eighty-one billion, seven hundred twenty-three million, six hundred twenty-one thousand, four hundred thirty-seven".