27721561 has 4 divisors (see below), whose sum is σ = 31681792. Its totient is φ = 23761332.

The previous prime is 27721487. The next prime is 27721567. The reversal of 27721561 is 16512772.

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 27721561 - 2²³ = 19332953 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (27721567) 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 3 ways as a sum of consecutive naturals, for example, 1980105 + ... + 1980118.

It is an arithmetic number, because the mean of its divisors is an integer number (7920448).

Almost surely, 2^27721561 is an apocalyptic number.

It is an amenable number.

27721561 is a deficient number, since it is larger than the sum of its proper divisors (3960231).

27721561 is an equidigital number, since it uses as much as digits as its factorization.

27721561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3960230.

The product of its digits is 5880, while the sum is 31.

The square root of 27721561 is about 5265.1268740649. The cubic root of 27721561 is about 302.6489888297.

It can be divided in two parts, 27721 and 561, that added together give a palindrome (28282).

The spelling of 27721561 in words is "twenty-seven million, seven hundred twenty-one thousand, five hundred sixty-one".