81639261 has 24 divisors (see below), whose sum is σ = 129078144. Its totient is φ = 49311360.

The previous prime is 81639251. The next prime is 81639281. The reversal of 81639261 is 16293618.

It is not a de Polignac number, because 81639261 - 2¹⁰ = 81638237 is a prime.

It is a super-2 number, since 2×81639261² = 13329937873252242, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81639221) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 32140 + ... + 34586.

It is an arithmetic number, because the mean of its divisors is an integer number (5378256).

Almost surely, 2^81639261 is an apocalyptic number.

It is an amenable number.

81639261 is a deficient number, since it is larger than the sum of its proper divisors (47438883).

81639261 is a wasteful number, since it uses less digits than its factorization.

81639261 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2801 (or 2798 counting only the distinct ones).

The product of its digits is 15552, while the sum is 36.

The square root of 81639261 is about 9035.4447040530. Note that the first 3 decimals coincide. The cubic root of 81639261 is about 433.8101291677.

It can be divided in two parts, 8163 and 9261, that added together give a square (17424 = 132²).

The spelling of 81639261 in words is "eighty-one million, six hundred thirty-nine thousand, two hundred sixty-one".