81721368 has 24 divisors (see below), whose sum is σ = 221328900. Its totient is φ = 27240432.

The previous prime is 81721361. The next prime is 81721373. The reversal of 81721368 is 86312718.

It is a tau number, because it is divible by the number of its divisors (24).

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81721361) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 567438 + ... + 567581.

Almost surely, 2^81721368 is an apocalyptic number.

It is an amenable number.

81721368 is an abundant number, since it is smaller than the sum of its proper divisors (139607532).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

81721368 is a wasteful number, since it uses less digits than its factorization.

81721368 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1135031 (or 1135024 counting only the distinct ones).

The product of its digits is 16128, while the sum is 36.

The square root of 81721368 is about 9039.9871681325. The cubic root of 81721368 is about 433.9555122980.

It can be divided in two parts, 817213 and 68, that added together give a triangular number (817281 = T₁₂₇₈).

The spelling of 81721368 in words is "eighty-one million, seven hundred twenty-one thousand, three hundred sixty-eight".