21251689 has 2 divisors, whose sum is σ = 21251690. Its totient is φ = 21251688.

The previous prime is 21251669. The next prime is 21251719. The reversal of 21251689 is 98615212.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 12131289 + 9120400 = 3483^2 + 3020^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21251689 is a prime.

It is a plaindrome in base 16.

It is not a weakly prime, because it can be changed into another prime (21251669) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10625844 + 10625845.

It is an arithmetic number, because the mean of its divisors is an integer number (10625845).

Almost surely, 2^21251689 is an apocalyptic number.

It is an amenable number.

21251689 is a deficient number, since it is larger than the sum of its proper divisors (1).

21251689 is an equidigital number, since it uses as much as digits as its factorization.

21251689 is an evil number, because the sum of its binary digits is even.

The product of its digits is 8640, while the sum is 34.

The square root of 21251689 is about 4609.9554227780. The cubic root of 21251689 is about 276.9902510612.

The spelling of 21251689 in words is "twenty-one million, two hundred fifty-one thousand, six hundred eighty-nine".