20501209 has 4 divisors (see below), whose sum is σ = 21580240. Its totient is φ = 19422180.

The previous prime is 20501207. The next prime is 20501213. The reversal of 20501209 is 90210502.

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, and also an emirpimes, since its reverse is a distinct semiprime: 90210502 = 2 ⋅45105251.

It is not a de Polignac number, because 20501209 - 2¹ = 20501207 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (19), and also a Moran number because the ratio is a prime number: 1079011 = 20501209 / (2 + 0 + 5 + 0 + 1 + 2 + 0 + 9).

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20501203) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 539487 + ... + 539524.

It is an arithmetic number, because the mean of its divisors is an integer number (5395060).

Almost surely, 2^20501209 is an apocalyptic number.

It is an amenable number.

20501209 is a deficient number, since it is larger than the sum of its proper divisors (1079031).

20501209 is a wasteful number, since it uses less digits than its factorization.

20501209 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1079030.

The product of its (nonzero) digits is 180, while the sum is 19.

The square root of 20501209 is about 4527.8260788153. The cubic root of 20501209 is about 273.6905638844.

The spelling of 20501209 in words is "twenty million, five hundred one thousand, two hundred nine".