20785257781 has 2 divisors, whose sum is σ = 20785257782. Its totient is φ = 20785257780.

The previous prime is 20785257737. The next prime is 20785257799. The reversal of 20785257781 is 18775258702.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20727360900 + 57896881 = 143970^2 + 7609^2 .

It is a cyclic number.

It is not a de Polignac number, because 20785257781 - 2¹⁷ = 20785126709 is a prime.

It is a super-2 number, since 2×20785257781² (a number of 21 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20785252781) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10392628890 + 10392628891.

It is an arithmetic number, because the mean of its divisors is an integer number (10392628891).

Almost surely, 2^20785257781 is an apocalyptic number.

It is an amenable number.

20785257781 is a deficient number, since it is larger than the sum of its proper divisors (1).

20785257781 is an equidigital number, since it uses as much as digits as its factorization.

20785257781 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 2195200, while the sum is 52.

The spelling of 20785257781 in words is "twenty billion, seven hundred eighty-five million, two hundred fifty-seven thousand, seven hundred eighty-one".