900001561 has 2 divisors, whose sum is σ = 900001562. Its totient is φ = 900001560.

The previous prime is 900001547. The next prime is 900001603. The reversal of 900001561 is 165100009.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 867008025 + 32993536 = 29445^2 + 5744^2 .

It is an emirp because it is prime and its reverse (165100009) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 900001561 - 2⁹ = 900001049 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (900001961) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 450000780 + 450000781.

It is an arithmetic number, because the mean of its divisors is an integer number (450000781).

Almost surely, 2^900001561 is an apocalyptic number.

It is an amenable number.

900001561 is a deficient number, since it is larger than the sum of its proper divisors (1).

900001561 is an equidigital number, since it uses as much as digits as its factorization.

900001561 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 270, while the sum is 22.

The square root of 900001561 is about 30000.0260166554. The cubic root of 900001561 is about 965.4899428012.

The spelling of 900001561 in words is "nine hundred million, one thousand, five hundred sixty-one".