20781643 has 2 divisors, whose sum is σ = 20781644. Its totient is φ = 20781642.

The previous prime is 20781637. The next prime is 20781653. The reversal of 20781643 is 34618702.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 20781643 - 2¹⁷ = 20650571 is a prime.

It is a zygodrome in base 3.

It is not a weakly prime, because it can be changed into another prime (20781653) 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, 10390821 + 10390822.

It is an arithmetic number, because the mean of its divisors is an integer number (10390822).

Almost surely, 2^20781643 is an apocalyptic number.

20781643 is a deficient number, since it is larger than the sum of its proper divisors (1).

20781643 is an equidigital number, since it uses as much as digits as its factorization.

20781643 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 8064, while the sum is 31.

The square root of 20781643 is about 4558.6887369067. The cubic root of 20781643 is about 274.9328453102.

It can be divided in two parts, 2078 and 1643, that added together give a square (3721 = 61²).

The spelling of 20781643 in words is "twenty million, seven hundred eighty-one thousand, six hundred forty-three".