78457721 has 4 divisors (see below), whose sum is σ = 78562944. Its totient is φ = 78352500.

The previous prime is 78457693. The next prime is 78457739. The reversal of 78457721 is 12775487.

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 78457721 - 2⁶ = 78457657 is a prime.

It is a super-3 number, since 3×78457721³ (a number of 25 digits) contains 333 as substring. Note that it is a super-d number also for d = 2.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (78457121) 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, 51485 + ... + 52986.

It is an arithmetic number, because the mean of its divisors is an integer number (19640736).

Almost surely, 2^78457721 is an apocalyptic number.

It is an amenable number.

78457721 is a deficient number, since it is larger than the sum of its proper divisors (105223).

78457721 is a wasteful number, since it uses less digits than its factorization.

78457721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 105222.

The product of its digits is 109760, while the sum is 41.

The square root of 78457721 is about 8857.6363099870. The cubic root of 78457721 is about 428.1000017442.

The spelling of 78457721 in words is "seventy-eight million, four hundred fifty-seven thousand, seven hundred twenty-one".