1561581 has 18 divisors (see below), whose sum is σ = 2624622. Its totient is φ = 892080.

The previous prime is 1561579. The next prime is 1561589. The reversal of 1561581 is 1851651.

It can be written as a sum of positive squares in only one way, i.e., 1285956 + 275625 = 1134^2 + 525^2 .

It is not a de Polignac number, because 1561581 - 2¹ = 1561579 is a prime.

It is a super-2 number, since 2×1561581² = 4877070439122, which contains 22 as substring.

1561581 is a lucky number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1561589) by changing a digit.

It is a polite number, since it can be written in 17 ways as a sum of consecutive naturals, for example, 1330 + ... + 2211.

2^1561581 is an apocalyptic number.

It is an amenable number.

1561581 is a deficient number, since it is larger than the sum of its proper divisors (1063041).

1561581 is a wasteful number, since it uses less digits than its factorization.

1561581 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3561 (or 3551 counting only the distinct ones).

The product of its digits is 1200, while the sum is 27.

The square root of 1561581 is about 1249.6323459322. The cubic root of 1561581 is about 116.0169664046.

The spelling of 1561581 in words is "one million, five hundred sixty-one thousand, five hundred eighty-one".