78778781 has 4 divisors (see below), whose sum is σ = 81320064. Its totient is φ = 76237500.

The previous prime is 78778669. The next prime is 78778787. The reversal of 78778781 is 18787787.

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, and also an emirpimes, since its reverse is a distinct semiprime: 18787787 = 937 ⋅20051.

It is a cyclic number.

It is not a de Polignac number, because 78778781 - 2¹⁸ = 78516637 is a prime.

It is a super-2 number, since 2×78778781² = 12412192671691922, which contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (78778787) 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, 1270595 + ... + 1270656.

It is an arithmetic number, because the mean of its divisors is an integer number (20330016).

Almost surely, 2^78778781 is an apocalyptic number.

It is an amenable number.

78778781 is a deficient number, since it is larger than the sum of its proper divisors (2541283).

78778781 is a wasteful number, since it uses less digits than its factorization.

78778781 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2541282.

The product of its digits is 1229312, while the sum is 53.

The square root of 78778781 is about 8875.7411521517. The cubic root of 78778781 is about 428.6831554369.

The spelling of 78778781 in words is "seventy-eight million, seven hundred seventy-eight thousand, seven hundred eighty-one".