72218021 has 2 divisors, whose sum is σ = 72218022. Its totient is φ = 72218020.

The previous prime is 72218017. The next prime is 72218039. The reversal of 72218021 is 12081227.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 38925121 + 33292900 = 6239^2 + 5770^2 .

It is a cyclic number.

It is not a de Polignac number, because 72218021 - 2² = 72218017 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (72218011) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 36109010 + 36109011.

It is an arithmetic number, because the mean of its divisors is an integer number (36109011).

Almost surely, 2^72218021 is an apocalyptic number.

It is an amenable number.

72218021 is a deficient number, since it is larger than the sum of its proper divisors (1).

72218021 is an equidigital number, since it uses as much as digits as its factorization.

72218021 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 448, while the sum is 23.

The square root of 72218021 is about 8498.1186741537. The cubic root of 72218021 is about 416.4362507016.

Adding to 72218021 its reverse (12081227), we get a palindrome (84299248).

The spelling of 72218021 in words is "seventy-two million, two hundred eighteen thousand, twenty-one".