67721561 has 4 divisors (see below), whose sum is σ = 67917072. Its totient is φ = 67526052.

The previous prime is 67721551. The next prime is 67721569. The reversal of 67721561 is 16512776.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 67721561 - 2⁶ = 67721497 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (67721569) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 97235 + ... + 97928.

It is an arithmetic number, because the mean of its divisors is an integer number (16979268).

Almost surely, 2^67721561 is an apocalyptic number.

It is an amenable number.

67721561 is a deficient number, since it is larger than the sum of its proper divisors (195511).

67721561 is a wasteful number, since it uses less digits than its factorization.

67721561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 195510.

The product of its digits is 17640, while the sum is 35.

The square root of 67721561 is about 8229.3110890280. The cubic root of 67721561 is about 407.6076441634.

The spelling of 67721561 in words is "sixty-seven million, seven hundred twenty-one thousand, five hundred sixty-one".