81605237 has 18 divisors (see below), whose sum is σ = 98146134. Its totient is φ = 67651920.

The previous prime is 81605231. The next prime is 81605243. The reversal of 81605237 is 73250618.

It is a happy number.

It is an interprime number because it is at equal distance from previous prime (81605231) and next prime (81605243).

It can be written as a sum of positive squares in only one way, i.e., 67996516 + 13608721 = 8246^2 + 3689^2 .

It is not a de Polignac number, because 81605237 - 2²² = 77410933 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81605231) by changing a digit.

It is a polite number, since it can be written in 17 ways as a sum of consecutive naturals, for example, 46223 + ... + 47955.

It is an arithmetic number, because the mean of its divisors is an integer number (5452563).

Almost surely, 2^81605237 is an apocalyptic number.

It is an amenable number.

81605237 is a deficient number, since it is larger than the sum of its proper divisors (16540897).

81605237 is a wasteful number, since it uses less digits than its factorization.

81605237 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1809 (or 1771 counting only the distinct ones).

The product of its (nonzero) digits is 10080, while the sum is 32.

The square root of 81605237 is about 9033.5617006804. The cubic root of 81605237 is about 433.7498558524.

The spelling of 81605237 in words is "eighty-one million, six hundred five thousand, two hundred thirty-seven".