1661156551 has 4 divisors (see below), whose sum is σ = 1706052712. Its totient is φ = 1616260392.

The previous prime is 1661156473. The next prime is 1661156561. The reversal of 1661156551 is 1556511661.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 1556511661 = 1583 ⋅983267.

It is a cyclic number.

It is not a de Polignac number, because 1661156551 - 2¹¹ = 1661154503 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (37), and also a Moran number because the ratio is a prime number: 44896123 = 1661156551 / (1 + 6 + 6 + 1 + 1 + 5 + 6 + 5 + 5 + 1).

It is a Duffinian number.

It is a zygodrome in base 2.

It is a self number, because there is not a number n which added to its sum of digits gives 1661156551.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1661156561) 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, 22448025 + ... + 22448098.

It is an arithmetic number, because the mean of its divisors is an integer number (426513178).

Almost surely, 2^1661156551 is an apocalyptic number.

1661156551 is a deficient number, since it is larger than the sum of its proper divisors (44896161).

1661156551 is an equidigital number, since it uses as much as digits as its factorization.

1661156551 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 44896160.

The product of its digits is 27000, while the sum is 37.

The square root of 1661156551 is about 40757.2883175513. The cubic root of 1661156551 is about 1184.3230660491.

The spelling of 1661156551 in words is "one billion, six hundred sixty-one million, one hundred fifty-six thousand, five hundred fifty-one".