21720511 has 2 divisors, whose sum is σ = 21720512. Its totient is φ = 21720510.

The previous prime is 21720499. The next prime is 21720563. The reversal of 21720511 is 11502712.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21720511 - 2¹³ = 21712319 is a prime.

It is a super-3 number, since 3×21720511³ (a number of 23 digits) contains 333 as substring. Note that it is a super-d number also for d = 2.

It is a plaindrome in base 8.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21720571) 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, 10860255 + 10860256.

It is an arithmetic number, because the mean of its divisors is an integer number (10860256).

Almost surely, 2^21720511 is an apocalyptic number.

21720511 is a deficient number, since it is larger than the sum of its proper divisors (1).

21720511 is an equidigital number, since it uses as much as digits as its factorization.

21720511 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 140, while the sum is 19.

The square root of 21720511 is about 4660.5269015424. The cubic root of 21720511 is about 279.0122980324.

The spelling of 21720511 in words is "twenty-one million, seven hundred twenty thousand, five hundred eleven".