21742551 has 6 divisors (see below), whose sum is σ = 31405920. Its totient is φ = 14495028.

The previous prime is 21742493. The next prime is 21742571. The reversal of 21742551 is 15524712.

It is not a de Polignac number, because 21742551 - 2¹⁰ = 21741527 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21742571) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1207911 + ... + 1207928.

It is an arithmetic number, because the mean of its divisors is an integer number (5234320).

Almost surely, 2^21742551 is an apocalyptic number.

21742551 is a deficient number, since it is larger than the sum of its proper divisors (9663369).

21742551 is a wasteful number, since it uses less digits than its factorization.

21742551 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2415845 (or 2415842 counting only the distinct ones).

The product of its digits is 2800, while the sum is 27.

The square root of 21742551 is about 4662.8908415274. The cubic root of 21742551 is about 279.1066382355.

The spelling of 21742551 in words is "twenty-one million, seven hundred forty-two thousand, five hundred fifty-one".