21217289 has 2 divisors, whose sum is σ = 21217290. Its totient is φ = 21217288.

The previous prime is 21217277. The next prime is 21217307. The reversal of 21217289 is 98271212.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 19758025 + 1459264 = 4445^2 + 1208^2 .

It is a cyclic number.

It is not a de Polignac number, because 21217289 - 2⁸ = 21217033 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21217249) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10608644 + 10608645.

It is an arithmetic number, because the mean of its divisors is an integer number (10608645).

Almost surely, 2^21217289 is an apocalyptic number.

It is an amenable number.

21217289 is a deficient number, since it is larger than the sum of its proper divisors (1).

21217289 is an equidigital number, since it uses as much as digits as its factorization.

21217289 is an evil number, because the sum of its binary digits is even.

The product of its digits is 4032, while the sum is 32.

The square root of 21217289 is about 4606.2228560937. Note that the first 3 decimals coincide. The cubic root of 21217289 is about 276.8407161154.

The spelling of 21217289 in words is "twenty-one million, two hundred seventeen thousand, two hundred eighty-nine".