91978009 has 2 divisors, whose sum is σ = 91978010. Its totient is φ = 91978008.

The previous prime is 91978001. The next prime is 91978021. The reversal of 91978009 is 90087919.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 50979600 + 40998409 = 7140^2 + 6403^2 .

It is an emirp because it is prime and its reverse (90087919) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 91978009 - 2³ = 91978001 is a prime.

It is not a weakly prime, because it can be changed into another prime (91978001) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 45989004 + 45989005.

It is an arithmetic number, because the mean of its divisors is an integer number (45989005).

Almost surely, 2^91978009 is an apocalyptic number.

It is an amenable number.

91978009 is a deficient number, since it is larger than the sum of its proper divisors (1).

91978009 is an equidigital number, since it uses as much as digits as its factorization.

91978009 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 40824, while the sum is 43.

The square root of 91978009 is about 9590.5166179930. The cubic root of 91978009 is about 451.3997713933.

The spelling of 91978009 in words is "ninety-one million, nine hundred seventy-eight thousand, nine".