1978688721 has 8 divisors (see below), whose sum is σ = 2639064064. Its totient is φ = 1318719600.

The previous prime is 1978688717. The next prime is 1978688729. The reversal of 1978688721 is 1278868791.

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

It is not a de Polignac number, because 1978688721 - 2² = 1978688717 is a prime.

It is a super-2 number, since 2×1978688721² = 7830418109225231682, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1978688729) 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, 90001 + ... + 109806.

It is an arithmetic number, because the mean of its divisors is an integer number (329883008).

Almost surely, 2^1978688721 is an apocalyptic number.

It is an amenable number.

1978688721 is a deficient number, since it is larger than the sum of its proper divisors (660375343).

1978688721 is a wasteful number, since it uses less digits than its factorization.

1978688721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 203111.

The product of its digits is 2709504, while the sum is 57.

The square root of 1978688721 is about 44482.4540802326. The cubic root of 1978688721 is about 1255.4299719820.

The spelling of 1978688721 in words is "one billion, nine hundred seventy-eight million, six hundred eighty-eight thousand, seven hundred twenty-one".