21188004721 has 9 divisors (see below), whose sum is σ = 22945273281. Its totient is φ = 19556411472.

The previous prime is 21188004707. The next prime is 21188004743. The reversal of 21188004721 is 12740088112.

The square root of 21188004721 is 145561.

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

It can be written as a sum of positive squares in 4 ways, for example, as 8301214321 + 12886790400 = 91111^2 + 113520^2 .

It is a de Polignac number, because none of the positive numbers 2^k-21188004721 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21188004751) by changing a digit.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 1886695 + ... + 1897891.

It is an arithmetic number, because the mean of its divisors is an integer number (2549474809).

Almost surely, 2^21188004721 is an apocalyptic number.

21188004721 is the 145561-st square number.

21188004721 is the 72781-st centered octagonal number.

It is an amenable number.

21188004721 is a deficient number, since it is larger than the sum of its proper divisors (1757268560).

21188004721 is an frugal number, since it uses more digits than its factorization.

21188004721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 22420 (or 11210 counting only the distinct ones).

The product of its (nonzero) digits is 7168, while the sum is 34.

The spelling of 21188004721 in words is "twenty-one billion, one hundred eighty-eight million, four thousand, seven hundred twenty-one".