21366661 has 2 divisors, whose sum is σ = 21366662. Its totient is φ = 21366660.

The previous prime is 21366647. The next prime is 21366677. The reversal of 21366661 is 16666312.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 18105025 + 3261636 = 4255^2 + 1806^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21366661 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21366641) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10683330 + 10683331.

It is an arithmetic number, because the mean of its divisors is an integer number (10683331).

Almost surely, 2^21366661 is an apocalyptic number.

It is an amenable number.

21366661 is a deficient number, since it is larger than the sum of its proper divisors (1).

21366661 is an equidigital number, since it uses as much as digits as its factorization.

21366661 is an evil number, because the sum of its binary digits is even.

The product of its digits is 7776, while the sum is 31.

The square root of 21366661 is about 4622.4085712970. The cubic root of 21366661 is about 277.4888603055.

The spelling of 21366661 in words is "twenty-one million, three hundred sixty-six thousand, six hundred sixty-one".