20819781 has 32 divisors (see below), whose sum is σ = 33194880. Its totient is φ = 12849408.

The previous prime is 20819779. The next prime is 20819791. The reversal of 20819781 is 18791802.

It is not a de Polignac number, because 20819781 - 2¹ = 20819779 is a prime.

It is a super-2 number, since 2×20819781² = 866926561775922, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20819791) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 30415 + ... + 31091.

It is an arithmetic number, because the mean of its divisors is an integer number (1037340).

Almost surely, 2^20819781 is an apocalyptic number.

It is an amenable number.

20819781 is a deficient number, since it is larger than the sum of its proper divisors (12375099).

20819781 is a wasteful number, since it uses less digits than its factorization.

20819781 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 770 (or 764 counting only the distinct ones).

The product of its (nonzero) digits is 8064, while the sum is 36.

The square root of 20819781 is about 4562.8698206282. The cubic root of 20819781 is about 275.1009260406.

The spelling of 20819781 in words is "twenty million, eight hundred nineteen thousand, seven hundred eighty-one".