20718781 has 2 divisors, whose sum is σ = 20718782. Its totient is φ = 20718780.

The previous prime is 20718751. The next prime is 20718809. The reversal of 20718781 is 18781702.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19980900 + 737881 = 4470^2 + 859^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-20718781 is a prime.

It is a super-2 number, since 2×20718781² = 858535772251922, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20718701) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10359390 + 10359391.

It is an arithmetic number, because the mean of its divisors is an integer number (10359391).

Almost surely, 2^20718781 is an apocalyptic number.

It is an amenable number.

20718781 is a deficient number, since it is larger than the sum of its proper divisors (1).

20718781 is an equidigital number, since it uses as much as digits as its factorization.

20718781 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 34.

The square root of 20718781 is about 4551.7887692642. The cubic root of 20718781 is about 274.6553522677.

The spelling of 20718781 in words is "twenty million, seven hundred eighteen thousand, seven hundred eighty-one".