21571551 has 6 divisors (see below), whose sum is σ = 31158920. Its totient is φ = 14381028.

The previous prime is 21571513. The next prime is 21571577. The reversal of 21571551 is 15517512.

It is a de Polignac number, because none of the positive numbers 2^k-21571551 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 (21571591) 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, 1198411 + ... + 1198428.

Almost surely, 2^21571551 is an apocalyptic number.

21571551 is a deficient number, since it is larger than the sum of its proper divisors (9587369).

21571551 is a wasteful number, since it uses less digits than its factorization.

21571551 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2396845 (or 2396842 counting only the distinct ones).

The product of its digits is 1750, while the sum is 27.

The square root of 21571551 is about 4644.5183819208. The cubic root of 21571551 is about 278.3730091129.

It can be divided in two parts, 21571 and 551, that added together give a palindrome (22122).

The spelling of 21571551 in words is "twenty-one million, five hundred seventy-one thousand, five hundred fifty-one".