20781994 has 4 divisors (see below), whose sum is σ = 31172994. Its totient is φ = 10390996.

The previous prime is 20781931. The next prime is 20782031. The reversal of 20781994 is 49918702.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 49918702 = 2 ⋅24959351.

It can be written as a sum of positive squares in only one way, i.e., 17114769 + 3667225 = 4137^2 + 1915^2 .

It is a Smith number, since the sum of its digits (40) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5195497 + ... + 5195500.

Almost surely, 2^20781994 is an apocalyptic number.

20781994 is a deficient number, since it is larger than the sum of its proper divisors (10391000).

20781994 is a wasteful number, since it uses less digits than its factorization.

20781994 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10390999.

The product of its (nonzero) digits is 36288, while the sum is 40.

The square root of 20781994 is about 4558.7272346566. The cubic root of 20781994 is about 274.9343931648.

The spelling of 20781994 in words is "twenty million, seven hundred eighty-one thousand, nine hundred ninety-four".