20415551 has 4 divisors (see below), whose sum is σ = 21985992. Its totient is φ = 18845112.

The previous prime is 20415529. The next prime is 20415599. The reversal of 20415551 is 15551402.

It is a happy number.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 15551402 = 2 ⋅7775701.

It is a de Polignac number, because none of the positive numbers 2^k-20415551 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20415511) 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, 785201 + ... + 785226.

It is an arithmetic number, because the mean of its divisors is an integer number (5496498).

Almost surely, 2^20415551 is an apocalyptic number.

20415551 is a deficient number, since it is larger than the sum of its proper divisors (1570441).

20415551 is a wasteful number, since it uses less digits than its factorization.

20415551 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1570440.

The product of its (nonzero) digits is 1000, while the sum is 23.

The square root of 20415551 is about 4518.3571129339. The cubic root of 20415551 is about 273.3088544738.

Adding to 20415551 its reverse (15551402), we get a palindrome (35966953).

The spelling of 20415551 in words is "twenty million, four hundred fifteen thousand, five hundred fifty-one".