78687121 has 4 divisors (see below), whose sum is σ = 81400500. Its totient is φ = 75973744.

The previous prime is 78687097. The next prime is 78687131. The reversal of 78687121 is 12178687.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 12178687 = 47 ⋅259121.

It can be written as a sum of positive squares in 2 ways, for example, as 19704721 + 58982400 = 4439^2 + 7680^2 .

It is a cyclic number.

It is not a de Polignac number, because 78687121 - 2¹¹ = 78685073 is a prime.

It is a super-2 number, since 2×78687121² = 12383326022537282, which contains 22 as substring.

It is a Smith number, since the sum of its digits (40) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (78687131) 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, 1356646 + ... + 1356703.

It is an arithmetic number, because the mean of its divisors is an integer number (20350125).

Almost surely, 2^78687121 is an apocalyptic number.

It is an amenable number.

78687121 is a deficient number, since it is larger than the sum of its proper divisors (2713379).

78687121 is a wasteful number, since it uses less digits than its factorization.

78687121 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2713378.

The product of its digits is 37632, while the sum is 40.

The square root of 78687121 is about 8870.5761368696. The cubic root of 78687121 is about 428.5168316853.

The spelling of 78687121 in words is "seventy-eight million, six hundred eighty-seven thousand, one hundred twenty-one".