78724921 has 4 divisors (see below), whose sum is σ = 85881744. Its totient is φ = 71568100.

The previous prime is 78724897. The next prime is 78724951. The reversal of 78724921 is 12942787.

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 78724921 - 2⁵ = 78724889 is a prime.

It is a super-2 number, since 2×78724921² = 12395226372912482, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (78724951) 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, 3578395 + ... + 3578416.

It is an arithmetic number, because the mean of its divisors is an integer number (21470436).

Almost surely, 2^78724921 is an apocalyptic number.

It is an amenable number.

78724921 is a deficient number, since it is larger than the sum of its proper divisors (7156823).

78724921 is a wasteful number, since it uses less digits than its factorization.

78724921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7156822.

The product of its digits is 56448, while the sum is 40.

The square root of 78724921 is about 8872.7065205607. The cubic root of 78724921 is about 428.5854381822.

The spelling of 78724921 in words is "seventy-eight million, seven hundred twenty-four thousand, nine hundred twenty-one".