1681721944 has 24 divisors (see below), whose sum is σ = 3668042340. Its totient is φ = 720737808.

The previous prime is 1681721929. The next prime is 1681721963. The reversal of 1681721944 is 4491271861.

It is a super-2 number, since 2×1681721944² = 5656377393862278272, which contains 22 as substring.

It is a Smith number, since the sum of its digits (43) coincides with the sum of the digits of its prime factors.

It is a self number, because there is not a number n which added to its sum of digits gives 1681721944.

It is a congruent number.

It is an unprimeable number.

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 5 ways as a sum of consecutive naturals, for example, 2144662 + ... + 2145445.

Almost surely, 2^1681721944 is an apocalyptic number.

1681721944 is a gapful number since it is divisible by the number (14) formed by its first and last digit.

It is an amenable number.

1681721944 is an abundant number, since it is smaller than the sum of its proper divisors (1986320396).

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

1681721944 is a wasteful number, since it uses less digits than its factorization.

1681721944 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4290127 (or 4290116 counting only the distinct ones).

The product of its digits is 96768, while the sum is 43.

The square root of 1681721944 is about 41008.8032500340. The cubic root of 1681721944 is about 1189.1904066579.

The spelling of 1681721944 in words is "one billion, six hundred eighty-one million, seven hundred twenty-one thousand, nine hundred forty-four".