81281691 has 16 divisors (see below), whose sum is σ = 121487520. Its totient is φ = 53706240.

The previous prime is 81281687. The next prime is 81281713. The reversal of 81281691 is 19618218.

It is not a de Polignac number, because 81281691 - 2² = 81281687 is a prime.

It is not an unprimeable number, because it can be changed into a prime (81281671) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 10270 + ... + 16371.

It is an arithmetic number, because the mean of its divisors is an integer number (7592970).

Almost surely, 2^81281691 is an apocalyptic number.

81281691 is a deficient number, since it is larger than the sum of its proper divisors (40205829).

81281691 is a wasteful number, since it uses less digits than its factorization.

81281691 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 26763 (or 26757 counting only the distinct ones).

The product of its digits is 6912, while the sum is 36.

The square root of 81281691 is about 9015.6359176710. The cubic root of 81281691 is about 433.1758571117.

The spelling of 81281691 in words is "eighty-one million, two hundred eighty-one thousand, six hundred ninety-one".