71665921 has 2 divisors, whose sum is σ = 71665922. Its totient is φ = 71665920.

The previous prime is 71665889. The next prime is 71665927. The reversal of 71665921 is 12956617.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 68707521 + 2958400 = 8289^2 + 1720^2 .

It is an emirp because it is prime and its reverse (12956617) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 71665921 - 2⁵ = 71665889 is a prime.

It is not a weakly prime, because it can be changed into another prime (71665927) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 35832960 + 35832961.

It is an arithmetic number, because the mean of its divisors is an integer number (35832961).

Almost surely, 2^71665921 is an apocalyptic number.

It is an amenable number.

71665921 is a deficient number, since it is larger than the sum of its proper divisors (1).

71665921 is an equidigital number, since it uses as much as digits as its factorization.

71665921 is an evil number, because the sum of its binary digits is even.

The product of its digits is 22680, while the sum is 37.

The square root of 71665921 is about 8465.5726917911. The cubic root of 71665921 is about 415.3723295204.

The spelling of 71665921 in words is "seventy-one million, six hundred sixty-five thousand, nine hundred twenty-one".