1321561561 has 2 divisors, whose sum is σ = 1321561562. Its totient is φ = 1321561560.

The previous prime is 1321561541. The next prime is 1321561567. The reversal of 1321561561 is 1651651231.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 1168272400 + 153289161 = 34180^2 + 12381^2 .

It is a cyclic number.

It is not a de Polignac number, because 1321561561 - 2⁵ = 1321561529 is a prime.

It is not a weakly prime, because it can be changed into another prime (1321561567) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 660780780 + 660780781.

It is an arithmetic number, because the mean of its divisors is an integer number (660780781).

Almost surely, 2^1321561561 is an apocalyptic number.

It is an amenable number.

1321561561 is a deficient number, since it is larger than the sum of its proper divisors (1).

1321561561 is an equidigital number, since it uses as much as digits as its factorization.

1321561561 is an evil number, because the sum of its binary digits is even.

The product of its digits is 5400, while the sum is 31.

The square root of 1321561561 is about 36353.2881731488. The cubic root of 1321561561 is about 1097.3937087093.

The spelling of 1321561561 in words is "one billion, three hundred twenty-one million, five hundred sixty-one thousand, five hundred sixty-one".