81556681 has 4 divisors (see below), whose sum is σ = 83453392. Its totient is φ = 79659972.

The previous prime is 81556679. The next prime is 81556687. The reversal of 81556681 is 18665518.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 18665518 = 2 ⋅9332759.

It is a cyclic number.

It is not a de Polignac number, because 81556681 - 2¹ = 81556679 is a prime.

It is a super-2 number, since 2×81556681² = 13302984431471522, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81556687) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 948291 + ... + 948376.

It is an arithmetic number, because the mean of its divisors is an integer number (20863348).

Almost surely, 2^81556681 is an apocalyptic number.

It is an amenable number.

81556681 is a deficient number, since it is larger than the sum of its proper divisors (1896711).

81556681 is a wasteful number, since it uses less digits than its factorization.

81556681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1896710.

The product of its digits is 57600, while the sum is 40.

The square root of 81556681 is about 9030.8737672498. The cubic root of 81556681 is about 433.6638101631.

The spelling of 81556681 in words is "eighty-one million, five hundred fifty-six thousand, six hundred eighty-one".