1661551 has 4 divisors (see below), whose sum is σ = 1678104. Its totient is φ = 1645000.

The previous prime is 1661549. The next prime is 1661557. The reversal of 1661551 is 1551661.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 1661551 - 2¹ = 1661549 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1661557) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 8125 + ... + 8326.

It is an arithmetic number, because the mean of its divisors is an integer number (419526).

2^1661551 is an apocalyptic number.

1661551 is a deficient number, since it is larger than the sum of its proper divisors (16553).

1661551 is a wasteful number, since it uses less digits than its factorization.

1661551 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 16552.

The product of its digits is 900, while the sum is 25.

The square root of 1661551 is about 1289.0116368753. The cubic root of 1661551 is about 118.4416799554.

The spelling of 1661551 in words is "one million, six hundred sixty-one thousand, five hundred fifty-one".