1216561 has 2 divisors, whose sum is σ = 1216562. Its totient is φ = 1216560.

The previous prime is 1216559. The next prime is 1216577. The reversal of 1216561 is 1656121.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1210000 + 6561 = 1100^2 + 81^2 .

It is an emirp because it is prime and its reverse (1656121) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 1216561 - 2¹ = 1216559 is a prime.

Together with 1216559, it forms a pair of twin primes.

It is a Chen prime.

It is an alternating number because its digits alternate between odd and even.

1216561 is a lucky number.

It is not a weakly prime, because it can be changed into another prime (1216591) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 608280 + 608281.

It is an arithmetic number, because the mean of its divisors is an integer number (608281).

2^1216561 is an apocalyptic number.

It is an amenable number.

1216561 is a deficient number, since it is larger than the sum of its proper divisors (1).

1216561 is an equidigital number, since it uses as much as digits as its factorization.

1216561 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 360, while the sum is 22.

The square root of 1216561 is about 1102.9782409458. The cubic root of 1216561 is about 106.7524776065.

It can be divided in two parts, 121 and 6561, that multiplied together give a square (793881 = 891²).

The spelling of 1216561 in words is "one million, two hundred sixteen thousand, five hundred sixty-one".