1661273856 has 324 divisors, whose sum is σ = 5407136280. Its totient is φ = 489984000.

The previous prime is 1661273851. The next prime is 1661273863. The reversal of 1661273856 is 6583721661.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1661273851) by changing a digit.

It is a polite number, since it can be written in 35 ways as a sum of consecutive naturals, for example, 16448206 + ... + 16448306.

Almost surely, 2^1661273856 is an apocalyptic number.

1661273856 is a gapful number since it is divisible by the number (16) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 1661273856, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (2703568140).

1661273856 is an abundant number, since it is smaller than the sum of its proper divisors (3745862424).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

1661273856 is a wasteful number, since it uses less digits than its factorization.

1661273856 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 204 (or 176 counting only the distinct ones).

The product of its digits is 362880, while the sum is 45.

The square root of 1661273856 is about 40758.7273599164. The cubic root of 1661273856 is about 1184.3509429616.

The spelling of 1661273856 in words is "one billion, six hundred sixty-one million, two hundred seventy-three thousand, eight hundred fifty-six".