21118661 has 2 divisors, whose sum is σ = 21118662. Its totient is φ = 21118660.

The previous prime is 21118619. The next prime is 21118663. The reversal of 21118661 is 16681112.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18653761 + 2464900 = 4319^2 + 1570^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21118661 is a prime.

Together with 21118663, it forms a pair of twin primes.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21118661.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21118663) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10559330 + 10559331.

It is an arithmetic number, because the mean of its divisors is an integer number (10559331).

Almost surely, 2^21118661 is an apocalyptic number.

It is an amenable number.

21118661 is a deficient number, since it is larger than the sum of its proper divisors (1).

21118661 is an equidigital number, since it uses as much as digits as its factorization.

21118661 is an evil number, because the sum of its binary digits is even.

The product of its digits is 576, while the sum is 26.

The square root of 21118661 is about 4595.5044336830. The cubic root of 21118661 is about 276.4110875008.

Adding to 21118661 its reverse (16681112), we get a palindrome (37799773).

It can be divided in two parts, 2 and 1118661, that multiplied together give a palindrome (2237322).

The spelling of 21118661 in words is "twenty-one million, one hundred eighteen thousand, six hundred sixty-one".