72217561 has 4 divisors (see below), whose sum is σ = 77772772. Its totient is φ = 66662352.

The previous prime is 72217531. The next prime is 72217571. The reversal of 72217561 is 16571227.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 26574025 + 45643536 = 5155^2 + 6756^2 .

It is a cyclic number.

It is not a de Polignac number, because 72217561 - 2⁵ = 72217529 is a prime.

It is a super-2 number, since 2×72217561² = 10430752233577442, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (72217531) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2777586 + ... + 2777611.

It is an arithmetic number, because the mean of its divisors is an integer number (19443193).

Almost surely, 2^72217561 is an apocalyptic number.

It is an amenable number.

72217561 is a deficient number, since it is larger than the sum of its proper divisors (5555211).

72217561 is a wasteful number, since it uses less digits than its factorization.

72217561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5555210.

The product of its digits is 5880, while the sum is 31.

The square root of 72217561 is about 8498.0916092968. The cubic root of 72217561 is about 416.4353665221.

Adding to 72217561 its reverse (16571227), we get a palindrome (88788788).

The spelling of 72217561 in words is "seventy-two million, two hundred seventeen thousand, five hundred sixty-one".