1211545551 has 4 divisors (see below), whose sum is σ = 1615394072. Its totient is φ = 807697032.

The previous prime is 1211545549. The next prime is 1211545561. The reversal of 1211545551 is 1555451121.

It is a semiprime because it is the product of two primes.

It is not a de Polignac number, because 1211545551 - 2¹ = 1211545549 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 (1211545561) 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, 201924256 + ... + 201924261.

It is an arithmetic number, because the mean of its divisors is an integer number (403848518).

Almost surely, 2^1211545551 is an apocalyptic number.

1211545551 is a deficient number, since it is larger than the sum of its proper divisors (403848521).

1211545551 is an equidigital number, since it uses as much as digits as its factorization.

1211545551 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 403848520.

The product of its digits is 5000, while the sum is 30.

The square root of 1211545551 is about 34807.2629058936. The cubic root of 1211545551 is about 1066.0557469259.

Adding to 1211545551 its reverse (1555451121), we get a palindrome (2766996672).

The spelling of 1211545551 in words is "one billion, two hundred eleven million, five hundred forty-five thousand, five hundred fifty-one".