81521751 has 8 divisors (see below), whose sum is σ = 109010304. Its totient is φ = 54190520.

The previous prime is 81521717. The next prime is 81521771. The reversal of 81521751 is 15712518.

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

It is a cyclic number.

It is not a de Polignac number, because 81521751 - 2⁷ = 81521623 is a prime.

It is a super-2 number, since 2×81521751² = 13291591772212002, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81521771) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 38115 + ... + 40196.

It is an arithmetic number, because the mean of its divisors is an integer number (13626288).

Almost surely, 2^81521751 is an apocalyptic number.

81521751 is a deficient number, since it is larger than the sum of its proper divisors (27488553).

81521751 is a wasteful number, since it uses less digits than its factorization.

81521751 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 78661.

The product of its digits is 2800, while the sum is 30.

The square root of 81521751 is about 9028.9396387394. The cubic root of 81521751 is about 433.6018898733.

The spelling of 81521751 in words is "eighty-one million, five hundred twenty-one thousand, seven hundred fifty-one".