21664417 has 2 divisors, whose sum is σ = 21664418. Its totient is φ = 21664416.

The previous prime is 21664373. The next prime is 21664457. The reversal of 21664417 is 71446612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 17648401 + 4016016 = 4201^2 + 2004^2 .

It is a cyclic number.

It is not a de Polignac number, because 21664417 - 2²³ = 13275809 is a prime.

It is not a weakly prime, because it can be changed into another prime (21664457) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10832208 + 10832209.

It is an arithmetic number, because the mean of its divisors is an integer number (10832209).

Almost surely, 2^21664417 is an apocalyptic number.

It is an amenable number.

21664417 is a deficient number, since it is larger than the sum of its proper divisors (1).

21664417 is an equidigital number, since it uses as much as digits as its factorization.

21664417 is an evil number, because the sum of its binary digits is even.

The product of its digits is 8064, while the sum is 31.

The square root of 21664417 is about 4654.5050220190. The cubic root of 21664417 is about 278.7719045440.

The spelling of 21664417 in words is "twenty-one million, six hundred sixty-four thousand, four hundred seventeen".