78121 has 2 divisors, whose sum is σ = 78122. Its totient is φ = 78120.

The previous prime is 78101. The next prime is 78137. The reversal of 78121 is 12187.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 68121 + 10000 = 261^2 + 100^2 .

It is a cyclic number.

It is not a de Polignac number, because 78121 - 2¹³ = 69929 is a prime.

It is a super-2 number, since 2×78121² = 12205781282, which contains 22 as substring.

It is a Chen prime.

It is an alternating number because its digits alternate between odd and even.

It is the 280-th Hogben number.

It is a nialpdrome in base 5.

It is not a weakly prime, because it can be changed into another prime (78101) by changing a digit.

It is a nontrivial repunit in base 279.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 39060 + 39061.

It is an arithmetic number, because the mean of its divisors is an integer number (39061).

2⁷⁸¹²¹ is an apocalyptic number.

It is an amenable number.

78121 is a deficient number, since it is larger than the sum of its proper divisors (1).

78121 is an equidigital number, since it uses as much as digits as its factorization.

78121 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 112, while the sum is 19.

The square root of 78121 is about 279.5013416784. The cubic root of 78121 is about 42.7486690647.

It can be divided in two parts, 7 and 8121, that added together give a triangular number (8128 = T₁₂₇).

The spelling of 78121 in words is "seventy-eight thousand, one hundred twenty-one".