21651559 has 2 divisors, whose sum is σ = 21651560. Its totient is φ = 21651558.

The previous prime is 21651551. The next prime is 21651563. The reversal of 21651559 is 95515612.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21651559 - 2³ = 21651551 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21651551) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10825779 + 10825780.

It is an arithmetic number, because the mean of its divisors is an integer number (10825780).

Almost surely, 2^21651559 is an apocalyptic number.

21651559 is a deficient number, since it is larger than the sum of its proper divisors (1).

21651559 is an equidigital number, since it uses as much as digits as its factorization.

21651559 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 13500, while the sum is 34.

The square root of 21651559 is about 4653.1235745465. The cubic root of 21651559 is about 278.7167425316.

It can be divided in two parts, 2 and 1651559, that added together give a palindrome (1651561).

The spelling of 21651559 in words is "twenty-one million, six hundred fifty-one thousand, five hundred fifty-nine".