21181663 has 2 divisors, whose sum is σ = 21181664. Its totient is φ = 21181662.

The previous prime is 21181651. The next prime is 21181669. The reversal of 21181663 is 36618112.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21181663 - 2¹⁷ = 21050591 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21181669) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10590831 + 10590832.

It is an arithmetic number, because the mean of its divisors is an integer number (10590832).

Almost surely, 2^21181663 is an apocalyptic number.

21181663 is a deficient number, since it is larger than the sum of its proper divisors (1).

21181663 is an equidigital number, since it uses as much as digits as its factorization.

21181663 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1728, while the sum is 28.

The square root of 21181663 is about 4602.3540715595. The cubic root of 21181663 is about 276.6856813434.

Adding to 21181663 its reverse (36618112), we get a palindrome (57799775).

The spelling of 21181663 in words is "twenty-one million, one hundred eighty-one thousand, six hundred sixty-three".