20509551 has 16 divisors (see below), whose sum is σ = 30507520. Its totient is φ = 13617720.

The previous prime is 20509547. The next prime is 20509591. The reversal of 20509551 is 15590502.

It is not a de Polignac number, because 20509551 - 2² = 20509547 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20509591) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 5916 + ... + 8718.

It is an arithmetic number, because the mean of its divisors is an integer number (1906720).

Almost surely, 2^20509551 is an apocalyptic number.

20509551 is a deficient number, since it is larger than the sum of its proper divisors (9997969).

20509551 is a wasteful number, since it uses less digits than its factorization.

20509551 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3083 (or 3077 counting only the distinct ones).

The product of its (nonzero) digits is 2250, while the sum is 27.

The square root of 20509551 is about 4528.7471777524. The cubic root of 20509551 is about 273.7276806723.

The spelling of 20509551 in words is "twenty million, five hundred nine thousand, five hundred fifty-one".