21668401 has 2 divisors, whose sum is σ = 21668402. Its totient is φ = 21668400.

The previous prime is 21668389. The next prime is 21668429. The reversal of 21668401 is 10486612.

It is an a-pointer prime, because the next prime (21668429) can be obtained adding 21668401 to its sum of digits (28).

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 12960000 + 8708401 = 3600^2 + 2951^2 .

It is a cyclic number.

It is not a de Polignac number, because 21668401 - 2²³ = 13279793 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21668401.

It is not a weakly prime, because it can be changed into another prime (21668201) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10834200 + 10834201.

It is an arithmetic number, because the mean of its divisors is an integer number (10834201).

Almost surely, 2^21668401 is an apocalyptic number.

It is an amenable number.

21668401 is a deficient number, since it is larger than the sum of its proper divisors (1).

21668401 is an equidigital number, since it uses as much as digits as its factorization.

21668401 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 2304, while the sum is 28.

The square root of 21668401 is about 4654.9329748128. The cubic root of 21668401 is about 278.7889918442.

It can be divided in two parts, 21668 and 401, that multiplied together give a palindrome (8688868).

The spelling of 21668401 in words is "twenty-one million, six hundred sixty-eight thousand, four hundred one".