21288997 has 2 divisors, whose sum is σ = 21288998. Its totient is φ = 21288996.

The previous prime is 21288991. The next prime is 21289001. The reversal of 21288997 is 79988212.

It is a Cunningham number, because it is equal to 4614²+1.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21288996 + 1 = 4614^2 + 1^2 .

It is a cyclic number.

It is not a de Polignac number, because 21288997 - 2³ = 21288989 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21288991) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10644498 + 10644499.

It is an arithmetic number, because the mean of its divisors is an integer number (10644499).

Almost surely, 2^21288997 is an apocalyptic number.

It is an amenable number.

21288997 is a deficient number, since it is larger than the sum of its proper divisors (1).

21288997 is an equidigital number, since it uses as much as digits as its factorization.

21288997 is an evil number, because the sum of its binary digits is even.

The product of its digits is 145152, while the sum is 46.

The square root of 21288997 is about 4614.0001083658. Note that the first 3 decimals coincide. The cubic root of 21288997 is about 277.1522446324.

The spelling of 21288997 in words is "twenty-one million, two hundred eighty-eight thousand, nine hundred ninety-seven".