81651 has 8 divisors (see below), whose sum is σ = 115344. Its totient is φ = 51200.

The previous prime is 81649. The next prime is 81667. The reversal of 81651 is 15618.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a 11-Lehmer number, since φ(81651) divides (81651-1)¹¹.

It is a cyclic number.

It is not a de Polignac number, because 81651 - 2¹ = 81649 is a prime.

It is an Ulam number.

It is not an unprimeable number, because it can be changed into a prime (81611) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 750 + ... + 851.

It is an arithmetic number, because the mean of its divisors is an integer number (14418).

2⁸¹⁶⁵¹ is an apocalyptic number.

81651 is a deficient number, since it is larger than the sum of its proper divisors (33693).

81651 is a wasteful number, since it uses less digits than its factorization.

81651 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1621.

The product of its digits is 240, while the sum is 21.

The square root of 81651 is about 285.7463910533. The cubic root of 81651 is about 43.3830920851.

It can be divided in two parts, 816 and 51, that multiplied together give a triangular number (41616 = T₂₈₈).

The spelling of 81651 in words is "eighty-one thousand, six hundred fifty-one".