21720350551 has 2 divisors, whose sum is σ = 21720350552. Its totient is φ = 21720350550.

The previous prime is 21720350521. The next prime is 21720350563. The reversal of 21720350551 is 15505302712.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21720350551 - 2⁷ = 21720350423 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21720350521) 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, 10860175275 + 10860175276.

It is an arithmetic number, because the mean of its divisors is an integer number (10860175276).

Almost surely, 2^21720350551 is an apocalyptic number.

21720350551 is a deficient number, since it is larger than the sum of its proper divisors (1).

21720350551 is an equidigital number, since it uses as much as digits as its factorization.

21720350551 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 10500, while the sum is 31.

The spelling of 21720350551 in words is "twenty-one billion, seven hundred twenty million, three hundred fifty thousand, five hundred fifty-one".