1815561 has 16 divisors (see below), whose sum is σ = 2934720. Its totient is φ = 1100160.

The previous prime is 1815559. The next prime is 1815587. The reversal of 1815561 is 1655181.

It is not a de Polignac number, because 1815561 - 2¹ = 1815559 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1815061) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 2760 + ... + 3353.

It is an arithmetic number, because the mean of its divisors is an integer number (183420).

2^1815561 is an apocalyptic number.

1815561 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

It is an amenable number.

1815561 is a deficient number, since it is larger than the sum of its proper divisors (1119159).

1815561 is a wasteful number, since it uses less digits than its factorization.

1815561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6133 (or 6127 counting only the distinct ones).

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

The square root of 1815561 is about 1347.4275490727. The cubic root of 1815561 is about 121.9935721777.

The spelling of 1815561 in words is "one million, eight hundred fifteen thousand, five hundred sixty-one".