20781017781 has 16 divisors (see below), whose sum is σ = 27756182784. Its totient is φ = 13829958144.

The previous prime is 20781017779. The next prime is 20781017797. The reversal of 20781017781 is 18771018702.

It is not a de Polignac number, because 20781017781 - 2¹ = 20781017779 is a prime.

It is a super-2 number, since 2×20781017781² (a number of 21 digits) contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20781017381) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 5573940 + ... + 5577666.

It is an arithmetic number, because the mean of its divisors is an integer number (1734761424).

Almost surely, 2^20781017781 is an apocalyptic number.

It is an amenable number.

20781017781 is a deficient number, since it is larger than the sum of its proper divisors (6975165003).

20781017781 is a wasteful number, since it uses less digits than its factorization.

20781017781 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6460.

The product of its (nonzero) digits is 43904, while the sum is 42.

The spelling of 20781017781 in words is "twenty billion, seven hundred eighty-one million, seventeen thousand, seven hundred eighty-one".