20639681 has 4 divisors (see below), whose sum is σ = 21726000. Its totient is φ = 19553364.

The previous prime is 20639669. The next prime is 20639701. The reversal of 20639681 is 18693602.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 20639681 - 2¹⁴ = 20623297 is a prime.

It is a super-2 number, since 2×20639681² = 851992863563522, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20639881) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 543131 + ... + 543168.

It is an arithmetic number, because the mean of its divisors is an integer number (5431500).

Almost surely, 2^20639681 is an apocalyptic number.

It is an amenable number.

20639681 is a deficient number, since it is larger than the sum of its proper divisors (1086319).

20639681 is a wasteful number, since it uses less digits than its factorization.

20639681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1086318.

The product of its (nonzero) digits is 15552, while the sum is 35.

The square root of 20639681 is about 4543.0915685247. The cubic root of 20639681 is about 274.3053808314.

The spelling of 20639681 in words is "twenty million, six hundred thirty-nine thousand, six hundred eighty-one".