21217743 has 6 divisors (see below), whose sum is σ = 30647864. Its totient is φ = 14145156.

The previous prime is 21217739. The next prime is 21217747. The reversal of 21217743 is 34771212.

It is a happy number.

It is an interprime number because it is at equal distance from previous prime (21217739) and next prime (21217747).

It is not a de Polignac number, because 21217743 - 2² = 21217739 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21217747) 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 in 5 ways as a sum of consecutive naturals, for example, 1178755 + ... + 1178772.

Almost surely, 2^21217743 is an apocalyptic number.

21217743 is a deficient number, since it is larger than the sum of its proper divisors (9430121).

21217743 is a wasteful number, since it uses less digits than its factorization.

21217743 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2357533 (or 2357530 counting only the distinct ones).

The product of its digits is 2352, while the sum is 27.

The square root of 21217743 is about 4606.2721369889. The cubic root of 21217743 is about 276.8426906810.

Adding to 21217743 its reverse (34771212), we get a palindrome (55988955).

It can be divided in two parts, 212 and 17743, that added together give a triangular number (17955 = T₁₈₉).

The spelling of 21217743 in words is "twenty-one million, two hundred seventeen thousand, seven hundred forty-three".