81721507 has 24 divisors (see below), whose sum is σ = 101132640. Its totient is φ = 64606080.

The previous prime is 81721501. The next prime is 81721511. The reversal of 81721507 is 70512718.

It is a happy number.

It is not a de Polignac number, because 81721507 - 2⁷ = 81721379 is a prime.

It is not an unprimeable number, because it can be changed into a prime (81721501) 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, 107007 + ... + 107767.

It is an arithmetic number, because the mean of its divisors is an integer number (4213860).

Almost surely, 2^81721507 is an apocalyptic number.

81721507 is a deficient number, since it is larger than the sum of its proper divisors (19411133).

81721507 is a wasteful number, since it uses less digits than its factorization.

81721507 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 843 (or 820 counting only the distinct ones).

The product of its (nonzero) digits is 3920, while the sum is 31.

The square root of 81721507 is about 9039.9948561932. The cubic root of 81721507 is about 433.9557583364.

It can be divided in two parts, 81721 and 507, that added together give a palindrome (82228).

The spelling of 81721507 in words is "eighty-one million, seven hundred twenty-one thousand, five hundred seven".