20643506 has 8 divisors (see below), whose sum is σ = 33347244. Its totient is φ = 9527760.

The previous prime is 20643487. The next prime is 20643509. The reversal of 20643506 is 60534602.

It can be written as a sum of positive squares in 2 ways, for example, as 19936225 + 707281 = 4465^2 + 841^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a Harshad number since it is a multiple of its sum of digits (26), and also a Moran number because the ratio is a prime number: 793981 = 20643506 / (2 + 0 + 6 + 4 + 3 + 5 + 0 + 6).

It is not an unprimeable number, because it can be changed into a prime (20643509) 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, 396965 + ... + 397016.

Almost surely, 2^20643506 is an apocalyptic number.

20643506 is a gapful number since it is divisible by the number (26) formed by its first and last digit.

20643506 is a deficient number, since it is larger than the sum of its proper divisors (12703738).

20643506 is a wasteful number, since it uses less digits than its factorization.

20643506 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 793996.

The product of its (nonzero) digits is 4320, while the sum is 26.

The square root of 20643506 is about 4543.5125178654. The cubic root of 20643506 is about 274.3223247831.

The spelling of 20643506 in words is "twenty million, six hundred forty-three thousand, five hundred six".