20781389 has 2 divisors, whose sum is σ = 20781390. Its totient is φ = 20781388.

The previous prime is 20781367. The next prime is 20781403. The reversal of 20781389 is 98318702.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 13801225 + 6980164 = 3715^2 + 2642^2 .

It is a cyclic number.

It is not a de Polignac number, because 20781389 - 2⁸ = 20781133 is a prime.

It is a super-2 number, since 2×20781389² = 863732257538642, which contains 22 as substring.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20781329) 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, 10390694 + 10390695.

It is an arithmetic number, because the mean of its divisors is an integer number (10390695).

Almost surely, 2^20781389 is an apocalyptic number.

It is an amenable number.

20781389 is a deficient number, since it is larger than the sum of its proper divisors (1).

20781389 is an equidigital number, since it uses as much as digits as its factorization.

20781389 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 24192, while the sum is 38.

The square root of 20781389 is about 4558.6608779333. The cubic root of 20781389 is about 274.9317251994.

The spelling of 20781389 in words is "twenty million, seven hundred eighty-one thousand, three hundred eighty-nine".