81521251 has 12 divisors (see below), whose sum is σ = 95676552. Its totient is φ = 69252288.

The previous prime is 81521213. The next prime is 81521281. The reversal of 81521251 is 15212518.

It is not a de Polignac number, because 81521251 - 2⁹ = 81520739 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81521201) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 1825 + ... + 12898.

It is an arithmetic number, because the mean of its divisors is an integer number (7973046).

Almost surely, 2^81521251 is an apocalyptic number.

81521251 is a deficient number, since it is larger than the sum of its proper divisors (14155301).

81521251 is a wasteful number, since it uses less digits than its factorization.

81521251 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 14850 (or 14843 counting only the distinct ones).

The product of its digits is 800, while the sum is 25.

The square root of 81521251 is about 9028.9119499528. The cubic root of 81521251 is about 433.6010033967.

Adding to 81521251 its reverse (15212518), we get a palindrome (96733769).

The spelling of 81521251 in words is "eighty-one million, five hundred twenty-one thousand, two hundred fifty-one".