216547981 has 6 divisors (see below), whose sum is σ = 234487050. Its totient is φ = 199890288.

The previous prime is 216547979. The next prime is 216547993. The reversal of 216547981 is 189745612.

It can be written as a sum of positive squares in 3 ways, for example, as 722500 + 215825481 = 850^2 + 14691^2 .

It is not a de Polignac number, because 216547981 - 2¹ = 216547979 is a prime.

It is a super-2 number, since 2×216547981² = 93786056150352722, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (216547081) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 640506 + ... + 640843.

It is an arithmetic number, because the mean of its divisors is an integer number (39081175).

Almost surely, 2^216547981 is an apocalyptic number.

It is an amenable number.

216547981 is a deficient number, since it is larger than the sum of its proper divisors (17939069).

216547981 is a wasteful number, since it uses less digits than its factorization.

216547981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1281375 (or 1281362 counting only the distinct ones).

The product of its digits is 120960, while the sum is 43.

The square root of 216547981 is about 14715.5693399882. The cubic root of 216547981 is about 600.5069613445.

The spelling of 216547981 in words is "two hundred sixteen million, five hundred forty-seven thousand, nine hundred eighty-one".