61728921 has 24 divisors (see below), whose sum is σ = 94784040. Its totient is φ = 38578176.

The previous prime is 61728917. The next prime is 61728959. The reversal of 61728921 is 12982716.

It can be written as a sum of positive squares in 4 ways, for example, as 7485696 + 54243225 = 2736^2 + 7365^2 .

It is not a de Polignac number, because 61728921 - 2² = 61728917 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (61728911) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 47245 + ... + 48533.

It is an arithmetic number, because the mean of its divisors is an integer number (3949335).

Almost surely, 2^61728921 is an apocalyptic number.

It is an amenable number.

61728921 is a deficient number, since it is larger than the sum of its proper divisors (33055119).

61728921 is a wasteful number, since it uses less digits than its factorization.

61728921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1625 (or 1622 counting only the distinct ones).

The product of its digits is 12096, while the sum is 36.

The square root of 61728921 is about 7856.7754836192. The cubic root of 61728921 is about 395.2114895862.

The spelling of 61728921 in words is "sixty-one million, seven hundred twenty-eight thousand, nine hundred twenty-one".