72178732921 has 3 divisors (see below), whose sum is σ = 72179001583. Its totient is φ = 72178464260.

The previous prime is 72178732919. The next prime is 72178732943. The reversal of 72178732921 is 12923787127.

The square root of 72178732921 is 268661.

It is a perfect power (a square), and thus also a powerful number.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in only one way, i.e., 44748748521 + 27429984400 = 211539^2 + 165620^2 .

It is not a de Polignac number, because 72178732921 - 2¹ = 72178732919 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (72178732721) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 2 ways as a sum of consecutive naturals, for example, 134331 + ... + 402991.

Almost surely, 2^72178732921 is an apocalyptic number.

72178732921 is the 268661-st square number.

72178732921 is the 134331-st centered octagonal number.

It is an amenable number.

72178732921 is a deficient number, since it is larger than the sum of its proper divisors (268662).

72178732921 is an frugal number, since it uses more digits than its factorization.

72178732921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 537322 (or 268661 counting only the distinct ones).

The product of its digits is 592704, while the sum is 49.

Multiplying 72178732921 by its sum of digits (49), we get a square (3536757913129 = 1880627²).

The spelling of 72178732921 in words is "seventy-two billion, one hundred seventy-eight million, seven hundred thirty-two thousand, nine hundred twenty-one".