81617661 has 18 divisors (see below), whose sum is σ = 119004990. Its totient is φ = 53901936.

The previous prime is 81617647. The next prime is 81617677. The reversal of 81617661 is 16671618.

It can be written as a sum of positive squares in only one way, i.e., 80192025 + 1425636 = 8955^2 + 1194^2 .

It is not a de Polignac number, because 81617661 - 2⁹ = 81617149 is a prime.

It is a super-2 number, since 2×81617661² = 13322885174221842, which contains 22 as substring.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81617611) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 17 ways as a sum of consecutive naturals, for example, 356295 + ... + 356523.

Almost surely, 2^81617661 is an apocalyptic number.

It is an amenable number.

81617661 is a deficient number, since it is larger than the sum of its proper divisors (37387329).

81617661 is a wasteful number, since it uses less digits than its factorization.

81617661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 633 (or 431 counting only the distinct ones).

The product of its digits is 12096, while the sum is 36.

The square root of 81617661 is about 9034.2493324017. The cubic root of 81617661 is about 433.7718668366.

The spelling of 81617661 in words is "eighty-one million, six hundred seventeen thousand, six hundred sixty-one".