71637721 has 2 divisors, whose sum is σ = 71637722. Its totient is φ = 71637720.

The previous prime is 71637719. The next prime is 71637739. The reversal of 71637721 is 12773617.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 70896400 + 741321 = 8420^2 + 861^2 .

It is a cyclic number.

It is not a de Polignac number, because 71637721 - 2¹ = 71637719 is a prime.

Together with 71637719, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (71637751) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 35818860 + 35818861.

It is an arithmetic number, because the mean of its divisors is an integer number (35818861).

Almost surely, 2^71637721 is an apocalyptic number.

It is an amenable number.

71637721 is a deficient number, since it is larger than the sum of its proper divisors (1).

71637721 is an equidigital number, since it uses as much as digits as its factorization.

71637721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 12348, while the sum is 34.

The square root of 71637721 is about 8463.9069583733. The cubic root of 71637721 is about 415.3178404119.

It can be divided in two parts, 7163 and 7721, that added together give a square (14884 = 122²).

The spelling of 71637721 in words is "seventy-one million, six hundred thirty-seven thousand, seven hundred twenty-one".