1981556720 has 320 divisors, whose sum is σ = 5993616384. Its totient is φ = 597442560.

The previous prime is 1981556693. The next prime is 1981556723. The reversal of 1981556720 is 276551891.

1981556720 = T₄₁₇ + T₄₁₈ + ... + T₂₂₈₆.

It is a Harshad number since it is a multiple of its sum of digits (44).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1981556723) by changing a digit.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 4472819 + ... + 4473261.

Almost surely, 2^1981556720 is an apocalyptic number.

1981556720 is a gapful number since it is divisible by the number (10) 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 1981556720, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (2996808192).

1981556720 is an abundant number, since it is smaller than the sum of its proper divisors (4012059664).

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

1981556720 is a wasteful number, since it uses less digits than its factorization.

1981556720 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 520 (or 514 counting only the distinct ones).

The product of its (nonzero) digits is 151200, while the sum is 44.

The square root of 1981556720 is about 44514.6798258732. The cubic root of 1981556720 is about 1256.0362377471.

The spelling of 1981556720 in words is "one billion, nine hundred eighty-one million, five hundred fifty-six thousand, seven hundred twenty".