81643208 has 8 divisors (see below), whose sum is σ = 153081030. Its totient is φ = 40821600.

The previous prime is 81643157. The next prime is 81643213. The reversal of 81643208 is 80234618.

It can be written as a sum of positive squares in only one way, i.e., 74684164 + 6959044 = 8642^2 + 2638^2 .

It is a tau number, because it is divible by the number of its divisors (8).

It is a super-2 number, since 2×81643208² = 13331226825062528, which contains 22 as substring.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5102693 + ... + 5102708.

Almost surely, 2^81643208 is an apocalyptic number.

It is an amenable number.

81643208 is a deficient number, since it is larger than the sum of its proper divisors (71437822).

81643208 is a wasteful number, since it uses less digits than its factorization.

81643208 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10205407 (or 10205403 counting only the distinct ones).

The product of its (nonzero) digits is 9216, while the sum is 32.

The square root of 81643208 is about 9035.6631189969. The cubic root of 81643208 is about 433.8171201708.

The spelling of 81643208 in words is "eighty-one million, six hundred forty-three thousand, two hundred eight".