1211616561 has 4 divisors (see below), whose sum is σ = 1615488752. Its totient is φ = 807744372.

The previous prime is 1211616557. The next prime is 1211616569. The reversal of 1211616561 is 1656161121.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 1656161121 = 3 ⋅552053707.

It is not a de Polignac number, because 1211616561 - 2² = 1211616557 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1211616569) 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, 201936091 + ... + 201936096.

It is an arithmetic number, because the mean of its divisors is an integer number (403872188).

Almost surely, 2^1211616561 is an apocalyptic number.

It is an amenable number.

1211616561 is a deficient number, since it is larger than the sum of its proper divisors (403872191).

1211616561 is an equidigital number, since it uses as much as digits as its factorization.

1211616561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 403872190.

The product of its digits is 2160, while the sum is 30.

The square root of 1211616561 is about 34808.2829366805. The cubic root of 1211616561 is about 1066.0765740806.

Adding to 1211616561 its reverse (1656161121), we get a palindrome (2867777682).

The spelling of 1211616561 in words is "one billion, two hundred eleven million, six hundred sixteen thousand, five hundred sixty-one".