21720821027 has 2 divisors, whose sum is σ = 21720821028. Its totient is φ = 21720821026.

The previous prime is 21720821021. The next prime is 21720821123. The reversal of 21720821027 is 72012802712.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21720821027 - 2¹⁶ = 21720755491 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21720820984 and 21720821002.

It is not a weakly prime, because it can be changed into another prime (21720821021) 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 as a sum of consecutive naturals, namely, 10860410513 + 10860410514.

It is an arithmetic number, because the mean of its divisors is an integer number (10860410514).

Almost surely, 2^21720821027 is an apocalyptic number.

21720821027 is a deficient number, since it is larger than the sum of its proper divisors (1).

21720821027 is an equidigital number, since it uses as much as digits as its factorization.

21720821027 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 6272, while the sum is 32.

The spelling of 21720821027 in words is "twenty-one billion, seven hundred twenty million, eight hundred twenty-one thousand, twenty-seven".