81563881 has 6 divisors (see below), whose sum is σ = 94880490. Its totient is φ = 69911856.

The previous prime is 81563879. The next prime is 81563899. The reversal of 81563881 is 18836518.

It can be written as a sum of positive squares in only one way, i.e., 81288256 + 275625 = 9016^2 + 525^2 .

It is not a de Polignac number, because 81563881 - 2¹ = 81563879 is a prime.

It is a super-2 number, since 2×81563881² = 13305333367564322, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81563381) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 832236 + ... + 832333.

It is an arithmetic number, because the mean of its divisors is an integer number (15813415).

Almost surely, 2^81563881 is an apocalyptic number.

It is an amenable number.

81563881 is a deficient number, since it is larger than the sum of its proper divisors (13316609).

81563881 is a wasteful number, since it uses less digits than its factorization.

81563881 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1664583 (or 1664576 counting only the distinct ones).

The product of its digits is 46080, while the sum is 40.

The square root of 81563881 is about 9031.2723909757. The cubic root of 81563881 is about 433.6765713803.

The spelling of 81563881 in words is "eighty-one million, five hundred sixty-three thousand, eight hundred eighty-one".