72661921 has 4 divisors (see below), whose sum is σ = 72695700. Its totient is φ = 72628144.

The previous prime is 72661891. The next prime is 72661933. The reversal of 72661921 is 12916627.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 48455521 + 24206400 = 6961^2 + 4920^2 .

It is a cyclic number.

It is not a de Polignac number, because 72661921 - 2⁷ = 72661793 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (72662921) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 13426 + ... + 18043.

It is an arithmetic number, because the mean of its divisors is an integer number (18173925).

Almost surely, 2^72661921 is an apocalyptic number.

It is an amenable number.

72661921 is a deficient number, since it is larger than the sum of its proper divisors (33779).

72661921 is a wasteful number, since it uses less digits than its factorization.

72661921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 33778.

The product of its digits is 9072, while the sum is 34.

The square root of 72661921 is about 8524.1962084410. The cubic root of 72661921 is about 417.2877398812.

The spelling of 72661921 in words is "seventy-two million, six hundred sixty-one thousand, nine hundred twenty-one".