78401891 has 4 divisors (see below), whose sum is σ = 79394400. Its totient is φ = 77409384.

The previous prime is 78401887. The next prime is 78401951. The reversal of 78401891 is 19810487.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 19810487 = 43 ⋅460709.

It is a cyclic number.

It is not a de Polignac number, because 78401891 - 2² = 78401887 is a prime.

It is a super-2 number, since 2×78401891² = 12293713024751762, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (78401831) 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, 496136 + ... + 496293.

It is an arithmetic number, because the mean of its divisors is an integer number (19848600).

Almost surely, 2^78401891 is an apocalyptic number.

78401891 is a deficient number, since it is larger than the sum of its proper divisors (992509).

78401891 is an equidigital number, since it uses as much as digits as its factorization.

78401891 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 992508.

The product of its (nonzero) digits is 16128, while the sum is 38.

The square root of 78401891 is about 8854.4842311678. The cubic root of 78401891 is about 427.9984332635.

The spelling of 78401891 in words is "seventy-eight million, four hundred one thousand, eight hundred ninety-one".