16638581 has 2 divisors, whose sum is σ = 16638582. Its totient is φ = 16638580.

The previous prime is 16638571. The next prime is 16638619. The reversal of 16638581 is 18583661.

It is a happy number.

It is an a-pointer prime, because the next prime (16638619) can be obtained adding 16638581 to its sum of digits (38).

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 12602500 + 4036081 = 3550^2 + 2009^2 .

It is a cyclic number.

It is not a de Polignac number, because 16638581 - 2¹⁰ = 16637557 is a prime.

It is a super-2 number, since 2×16638581² = 553684755387122, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (16638571) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 8319290 + 8319291.

It is an arithmetic number, because the mean of its divisors is an integer number (8319291).

Almost surely, 2^16638581 is an apocalyptic number.

It is an amenable number.

16638581 is a deficient number, since it is larger than the sum of its proper divisors (1).

16638581 is an equidigital number, since it uses as much as digits as its factorization.

16638581 is an evil number, because the sum of its binary digits is even.

The product of its digits is 34560, while the sum is 38.

The square root of 16638581 is about 4079.0416766687. The cubic root of 16638581 is about 255.2929147180.

The spelling of 16638581 in words is "sixteen million, six hundred thirty-eight thousand, five hundred eighty-one".