78209521 has 12 divisors (see below), whose sum is σ = 85121652. Its totient is φ = 71432928.

The previous prime is 78209507. The next prime is 78209533. The reversal of 78209521 is 12590287.

It can be written as a sum of positive squares in 2 ways, for example, as 25806400 + 52403121 = 5080^2 + 7239^2 .

It is not a de Polignac number, because 78209521 - 2¹⁷ = 78078449 is a prime.

It is a super-2 number, since 2×78209521² = 12233458350098882, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (78209581) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 209491 + ... + 209863.

It is an arithmetic number, because the mean of its divisors is an integer number (7093471).

Almost surely, 2^78209521 is an apocalyptic number.

It is an amenable number.

78209521 is a deficient number, since it is larger than the sum of its proper divisors (6912131).

78209521 is a wasteful number, since it uses less digits than its factorization.

78209521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 640 (or 513 counting only the distinct ones).

The product of its (nonzero) digits is 10080, while the sum is 34.

The square root of 78209521 is about 8843.6147021453. The cubic root of 78209521 is about 427.6480952429.

The spelling of 78209521 in words is "seventy-eight million, two hundred nine thousand, five hundred twenty-one".