21611173621721 has 2 divisors, whose sum is σ = 21611173621722. Its totient is φ = 21611173621720.

The previous prime is 21611173621673. The next prime is 21611173621781. The reversal of 21611173621721 is 12712637111612.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21218967024025 + 392206597696 = 4606405^2 + 626264^2 .

It is a cyclic number.

It is not a de Polignac number, because 21611173621721 - 2¹⁴ = 21611173605337 is a prime.

It is not a weakly prime, because it can be changed into another prime (21611173621781) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (29) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10805586810860 + 10805586810861.

It is an arithmetic number, because the mean of its divisors is an integer number (10805586810861).

Almost surely, 2^{21611173621721} is an apocalyptic number.

It is an amenable number.

21611173621721 is a deficient number, since it is larger than the sum of its proper divisors (1).

21611173621721 is an equidigital number, since it uses as much as digits as its factorization.

21611173621721 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 42336, while the sum is 41.

The spelling of 21611173621721 in words is "twenty-one trillion, six hundred eleven billion, one hundred seventy-three million, six hundred twenty-one thousand, seven hundred twenty-one".