1605221561 has 4 divisors (see below), whose sum is σ = 1605309732. Its totient is φ = 1605133392.

The previous prime is 1605221531. The next prime is 1605221573. The reversal of 1605221561 is 1651225061.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 883278400 + 721943161 = 29720^2 + 26869^2 .

It is a cyclic number.

It is not a de Polignac number, because 1605221561 - 2¹⁸ = 1604959417 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1605221521) 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, 5546 + ... + 56931.

It is an arithmetic number, because the mean of its divisors is an integer number (401327433).

Almost surely, 2^1605221561 is an apocalyptic number.

It is an amenable number.

1605221561 is a deficient number, since it is larger than the sum of its proper divisors (88171).

1605221561 is an equidigital number, since it uses as much as digits as its factorization.

1605221561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 88170.

The product of its (nonzero) digits is 3600, while the sum is 29.

The square root of 1605221561 is about 40065.2163478497. The cubic root of 1605221561 is about 1170.8780418006.

The spelling of 1605221561 in words is "one billion, six hundred five million, two hundred twenty-one thousand, five hundred sixty-one".