1623978721 has 4 divisors (see below), whose sum is σ = 1661745712. Its totient is φ = 1586211732.

The previous prime is 1623978701. The next prime is 1623978739. The reversal of 1623978721 is 1278793261.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 1623978721 - 2⁵ = 1623978689 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1623978701) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 18883431 + ... + 18883516.

It is an arithmetic number, because the mean of its divisors is an integer number (415436428).

Almost surely, 2^1623978721 is an apocalyptic number.

It is an amenable number.

1623978721 is a deficient number, since it is larger than the sum of its proper divisors (37766991).

1623978721 is an equidigital number, since it uses as much as digits as its factorization.

1623978721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 37766990.

The product of its digits is 254016, while the sum is 46.

The square root of 1623978721 is about 40298.6193435954. The cubic root of 1623978721 is about 1175.4209980158.

The spelling of 1623978721 in words is "one billion, six hundred twenty-three million, nine hundred seventy-eight thousand, seven hundred twenty-one".