72129309781 has 4 divisors (see below), whose sum is σ = 75265366752. Its totient is φ = 68993252812.

The previous prime is 72129309779. The next prime is 72129309803. The reversal of 72129309781 is 18790392127.

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 not a de Polignac number, because 72129309781 - 2¹ = 72129309779 is a prime.

It is a super-2 number, since 2×72129309781² (a number of 23 digits) contains 22 as substring.

It is a Smith number, since the sum of its digits (49) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (72129309731) 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, 1568028451 + ... + 1568028496.

It is an arithmetic number, because the mean of its divisors is an integer number (18816341688).

Almost surely, 2^72129309781 is an apocalyptic number.

It is an amenable number.

72129309781 is a deficient number, since it is larger than the sum of its proper divisors (3136056971).

72129309781 is a wasteful number, since it uses less digits than its factorization.

72129309781 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3136056970.

The product of its (nonzero) digits is 381024, while the sum is 49.

The spelling of 72129309781 in words is "seventy-two billion, one hundred twenty-nine million, three hundred nine thousand, seven hundred eighty-one".