81216145 has 4 divisors (see below), whose sum is σ = 97459380. Its totient is φ = 64972912.

The previous prime is 81216133. The next prime is 81216199. The reversal of 81216145 is 54161218.

It is a Cunningham number, because it is equal to 9012²+1.

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 29246464 + 51969681 = 5408^2 + 7209^2 .

It is a cyclic number.

It is not a de Polignac number, because 81216145 - 2¹¹ = 81214097 is a prime.

It is a super-2 number, since 2×81216145² = 13192124417322050, which contains 22 as substring.

It is an alternating number because its digits alternate between even and odd.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 8121610 + ... + 8121619.

It is an arithmetic number, because the mean of its divisors is an integer number (24364845).

Almost surely, 2^81216145 is an apocalyptic number.

It is an amenable number.

81216145 is a deficient number, since it is larger than the sum of its proper divisors (16243235).

81216145 is a wasteful number, since it uses less digits than its factorization.

81216145 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 16243234.

The product of its digits is 1920, while the sum is 28.

The square root of 81216145 is about 9012.0000554816. Note that the first 4 decimals coincide. The cubic root of 81216145 is about 433.0593873390.

The spelling of 81216145 in words is "eighty-one million, two hundred sixteen thousand, one hundred forty-five".