78391521 has 24 divisors (see below), whose sum is σ = 127248576. Its totient is φ = 46141920.

The previous prime is 78391507. The next prime is 78391559. The reversal of 78391521 is 12519387.

It is not a de Polignac number, because 78391521 - 2⁷ = 78391393 is a prime.

It is a super-2 number, since 2×78391521² = 12290461129386882, which contains 22 as substring.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (78391421) 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 in 23 ways as a sum of consecutive naturals, for example, 11875 + ... + 17256.

It is an arithmetic number, because the mean of its divisors is an integer number (5302024).

Almost surely, 2^78391521 is an apocalyptic number.

It is an amenable number.

78391521 is a deficient number, since it is larger than the sum of its proper divisors (48857055).

78391521 is a wasteful number, since it uses less digits than its factorization.

78391521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 29173 (or 29170 counting only the distinct ones).

The product of its digits is 15120, while the sum is 36.

The square root of 78391521 is about 8853.8986328058. The cubic root of 78391521 is about 427.9795623775.

The spelling of 78391521 in words is "seventy-eight million, three hundred ninety-one thousand, five hundred twenty-one".