1216564561 has 4 divisors (see below), whose sum is σ = 1221877300. Its totient is φ = 1211251824.

The previous prime is 1216564549. The next prime is 1216564567. The reversal of 1216564561 is 1654656121.

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

It can be written as a sum of positive squares in 2 ways, for example, as 1064782161 + 151782400 = 32631^2 + 12320^2 .

It is a cyclic number.

It is not a de Polignac number, because 1216564561 - 2⁹ = 1216564049 is a prime.

It is a super-2 number, since 2×1216564561² = 2960058662162245442, which contains 22 as substring.

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 1216564561.

It is not an unprimeable number, because it can be changed into a prime (1216564567) 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, 2656026 + ... + 2656483.

It is an arithmetic number, because the mean of its divisors is an integer number (305469325).

Almost surely, 2^1216564561 is an apocalyptic number.

It is an amenable number.

1216564561 is a deficient number, since it is larger than the sum of its proper divisors (5312739).

1216564561 is an equidigital number, since it uses as much as digits as its factorization.

1216564561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5312738.

The product of its digits is 43200, while the sum is 37.

The square root of 1216564561 is about 34879.2855574767. The cubic root of 1216564561 is about 1067.5258176492.

The spelling of 1216564561 in words is "one billion, two hundred sixteen million, five hundred sixty-four thousand, five hundred sixty-one".