20781634 has 4 divisors (see below), whose sum is σ = 31172454. Its totient is φ = 10390816.

The previous prime is 20781617. The next prime is 20781637. The reversal of 20781634 is 43618702.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in only one way, i.e., 20657025 + 124609 = 4545^2 + 353^2 .

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a junction number, because it is equal to n+sod(n) for n = 20781596 and 20781605.

It is not an unprimeable number, because it can be changed into a prime (20781637) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5195407 + ... + 5195410.

Almost surely, 2^20781634 is an apocalyptic number.

20781634 is a deficient number, since it is larger than the sum of its proper divisors (10390820).

20781634 is a wasteful number, since it uses less digits than its factorization.

20781634 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10390819.

The product of its (nonzero) digits is 8064, while the sum is 31.

The square root of 20781634 is about 4558.6877497806. The cubic root of 20781634 is about 274.9328056214.

The spelling of 20781634 in words is "twenty million, seven hundred eighty-one thousand, six hundred thirty-four".