1211780661 has 32 divisors (see below), whose sum is σ = 2012559360. Its totient is φ = 631468224.

The previous prime is 1211780629. The next prime is 1211780681. The reversal of 1211780661 is 1660871121.

It is a happy number.

It is not a de Polignac number, because 1211780661 - 2⁵ = 1211780629 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1211780611) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 4081 + ... + 49398.

It is an arithmetic number, because the mean of its divisors is an integer number (62892480).

Almost surely, 2^1211780661 is an apocalyptic number.

It is an amenable number.

1211780661 is a deficient number, since it is larger than the sum of its proper divisors (800778699).

1211780661 is a wasteful number, since it uses less digits than its factorization.

1211780661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 53585.

The product of its (nonzero) digits is 4032, while the sum is 33.

The square root of 1211780661 is about 34810.6400544431. The cubic root of 1211780661 is about 1066.1247013166.

The spelling of 1211780661 in words is "one billion, two hundred eleven million, seven hundred eighty thousand, six hundred sixty-one".