21971551 has 10 divisors (see below), whose sum is σ = 25634752. Its totient is φ = 18830700.

The previous prime is 21971549. The next prime is 21971563. The reversal of 21971551 is 15517912.

It is not a de Polignac number, because 21971551 - 2¹ = 21971549 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 (21971501) by changing a digit.

It is a polite number, since it can be written in 9 ways as a sum of consecutive naturals, for example, 2175 + ... + 6976.

Almost surely, 2^21971551 is an apocalyptic number.

21971551 is a deficient number, since it is larger than the sum of its proper divisors (3663201).

21971551 is an frugal number, since it uses more digits than its factorization.

21971551 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9179 (or 9158 counting only the distinct ones).

The product of its digits is 3150, while the sum is 31.

The square root of 21971551 is about 4687.3821051841. The cubic root of 21971551 is about 280.0831003345.

It can be divided in two parts, 21971 and 551, that added together give a palindrome (22522).

The spelling of 21971551 in words is "twenty-one million, nine hundred seventy-one thousand, five hundred fifty-one".