20719981 has 2 divisors, whose sum is σ = 20719982. Its totient is φ = 20719980.

The previous prime is 20719973. The next prime is 20720027. The reversal of 20719981 is 18991702.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17147881 + 3572100 = 4141^2 + 1890^2 .

It is a cyclic number.

It is not a de Polignac number, because 20719981 - 2³ = 20719973 is a prime.

It is a super-2 number, since 2×20719981² = 858635225280722, which contains 22 as substring.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 20719981.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20719921) 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, 10359990 + 10359991.

It is an arithmetic number, because the mean of its divisors is an integer number (10359991).

Almost surely, 2^20719981 is an apocalyptic number.

It is an amenable number.

20719981 is a deficient number, since it is larger than the sum of its proper divisors (1).

20719981 is an equidigital number, since it uses as much as digits as its factorization.

20719981 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 9072, while the sum is 37.

The square root of 20719981 is about 4551.9205836658. The cubic root of 20719981 is about 274.6606547042.

The spelling of 20719981 in words is "twenty million, seven hundred nineteen thousand, nine hundred eighty-one".