1678945721 has 8 divisors (see below), whose sum is σ = 1778091264. Its totient is φ = 1579842880.

The previous prime is 1678945717. The next prime is 1678945727. The reversal of 1678945721 is 1275498761.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 1678945721 - 2² = 1678945717 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 1678945721.

It is not an unprimeable number, because it can be changed into a prime (1678945727) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 108176 + ... + 122718.

It is an arithmetic number, because the mean of its divisors is an integer number (222261408).

Almost surely, 2^1678945721 is an apocalyptic number.

It is an amenable number.

1678945721 is a deficient number, since it is larger than the sum of its proper divisors (99145543).

1678945721 is a wasteful number, since it uses less digits than its factorization.

1678945721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 21351.

The product of its digits is 846720, while the sum is 50.

The square root of 1678945721 is about 40974.9401585896. The cubic root of 1678945721 is about 1188.5356658145.

The spelling of 1678945721 in words is "one billion, six hundred seventy-eight million, nine hundred forty-five thousand, seven hundred twenty-one".