21721111187 has 2 divisors, whose sum is σ = 21721111188. Its totient is φ = 21721111186.

The previous prime is 21721111121. The next prime is 21721111267. The reversal of 21721111187 is 78111112712.

It is a happy number.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21721111187 - 2¹² = 21721107091 is a prime.

It is not a weakly prime, because it can be changed into another prime (21721111787) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10860555593 + 10860555594.

It is an arithmetic number, because the mean of its divisors is an integer number (10860555594).

Almost surely, 2^21721111187 is an apocalyptic number.

21721111187 is a deficient number, since it is larger than the sum of its proper divisors (1).

21721111187 is an equidigital number, since it uses as much as digits as its factorization.

21721111187 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1568, while the sum is 32.

Adding to 21721111187 its reverse (78111112712), we get a palindrome (99832223899).

The spelling of 21721111187 in words is "twenty-one billion, seven hundred twenty-one million, one hundred eleven thousand, one hundred eighty-seven".