20781559 has 2 divisors, whose sum is σ = 20781560. Its totient is φ = 20781558.

The previous prime is 20781557. The next prime is 20781583. The reversal of 20781559 is 95518702.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 20781559 - 2¹ = 20781557 is a prime.

Together with 20781557, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20781557) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10390779 + 10390780.

It is an arithmetic number, because the mean of its divisors is an integer number (10390780).

Almost surely, 2^20781559 is an apocalyptic number.

20781559 is a deficient number, since it is larger than the sum of its proper divisors (1).

20781559 is an equidigital number, since it uses as much as digits as its factorization.

20781559 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 25200, while the sum is 37.

The square root of 20781559 is about 4558.6795237218. The cubic root of 20781559 is about 274.9324748809.

The spelling of 20781559 in words is "twenty million, seven hundred eighty-one thousand, five hundred fifty-nine".