78121657 has 2 divisors, whose sum is σ = 78121658. Its totient is φ = 78121656.

The previous prime is 78121651. The next prime is 78121697. The reversal of 78121657 is 75612187.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 71588521 + 6533136 = 8461^2 + 2556^2 .

It is a cyclic number.

It is not a de Polignac number, because 78121657 - 2³ = 78121649 is a prime.

It is a super-2 number, since 2×78121657² = 12205986584851298, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (78121651) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 39060828 + 39060829.

It is an arithmetic number, because the mean of its divisors is an integer number (39060829).

Almost surely, 2^78121657 is an apocalyptic number.

It is an amenable number.

78121657 is a deficient number, since it is larger than the sum of its proper divisors (1).

78121657 is an equidigital number, since it uses as much as digits as its factorization.

78121657 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 23520, while the sum is 37.

The square root of 78121657 is about 8838.6456541712. The cubic root of 78121657 is about 427.4878890360.

The spelling of 78121657 in words is "seventy-eight million, one hundred twenty-one thousand, six hundred fifty-seven".