661551211 has 4 divisors (see below), whose sum is σ = 662932800. Its totient is φ = 660169624.

The previous prime is 661551203. The next prime is 661551221. The reversal of 661551211 is 112155166.

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: 112155166 = 2 ⋅56077583.

It is a cyclic number.

It is not a de Polignac number, because 661551211 - 2³ = 661551203 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 661551211.

It is not an unprimeable number, because it can be changed into a prime (661551221) 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, 690076 + ... + 691033.

It is an arithmetic number, because the mean of its divisors is an integer number (165733200).

Almost surely, 2^661551211 is an apocalyptic number.

661551211 is a deficient number, since it is larger than the sum of its proper divisors (1381589).

661551211 is a wasteful number, since it uses less digits than its factorization.

661551211 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1381588.

The product of its digits is 1800, while the sum is 28.

The square root of 661551211 is about 25720.6378420132. The cubic root of 661551211 is about 871.3403442409.

The spelling of 661551211 in words is "six hundred sixty-one million, five hundred fifty-one thousand, two hundred eleven".