21689497 has 2 divisors, whose sum is σ = 21689498. Its totient is φ = 21689496.

The previous prime is 21689471. The next prime is 21689509. The reversal of 21689497 is 79498612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 16941456 + 4748041 = 4116^2 + 2179^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21689497 is a prime.

It is a super-2 number, since 2×21689497² = 940868560226018, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21689407) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10844748 + 10844749.

It is an arithmetic number, because the mean of its divisors is an integer number (10844749).

Almost surely, 2^21689497 is an apocalyptic number.

It is an amenable number.

21689497 is a deficient number, since it is larger than the sum of its proper divisors (1).

21689497 is an equidigital number, since it uses as much as digits as its factorization.

21689497 is an odious number, because the sum of its binary digits is odd.

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

The square root of 21689497 is about 4657.1984067677. The cubic root of 21689497 is about 278.8794372959.

The spelling of 21689497 in words is "twenty-one million, six hundred eighty-nine thousand, four hundred ninety-seven".