21648997 has 2 divisors, whose sum is σ = 21648998. Its totient is φ = 21648996.

The previous prime is 21648947. The next prime is 21649031. The reversal of 21648997 is 79984612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18267076 + 3381921 = 4274^2 + 1839^2 .

It is a cyclic number.

It is not a de Polignac number, because 21648997 - 2¹⁹ = 21124709 is a prime.

It is a super-2 number, since 2×21648997² = 937358142212018, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21648937) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10824498 + 10824499.

It is an arithmetic number, because the mean of its divisors is an integer number (10824499).

Almost surely, 2^21648997 is an apocalyptic number.

It is an amenable number.

21648997 is a deficient number, since it is larger than the sum of its proper divisors (1).

21648997 is an equidigital number, since it uses as much as digits as its factorization.

21648997 is an evil number, because the sum of its binary digits is even.

The product of its digits is 217728, while the sum is 46.

The square root of 21648997 is about 4652.8482674594. The cubic root of 21648997 is about 278.7057487049.

The spelling of 21648997 in words is "twenty-one million, six hundred forty-eight thousand, nine hundred ninety-seven".