21505071 has 16 divisors (see below), whose sum is σ = 33440000. Its totient is φ = 12288024.

The previous prime is 21505063. The next prime is 21505109. The reversal of 21505071 is 17050512.

It is not a de Polignac number, because 21505071 - 2³ = 21505063 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (21).

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21505171) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 9421 + ... + 11478.

It is an arithmetic number, because the mean of its divisors is an integer number (2090000).

Almost surely, 2^21505071 is an apocalyptic number.

21505071 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

21505071 is a deficient number, since it is larger than the sum of its proper divisors (11934929).

21505071 is an equidigital number, since it uses as much as digits as its factorization.

21505071 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 20923 (or 20909 counting only the distinct ones).

The product of its (nonzero) digits is 350, while the sum is 21.

The square root of 21505071 is about 4637.3560355013. The cubic root of 21505071 is about 278.0867481122.

Adding to 21505071 its reverse (17050512), we get a palindrome (38555583).

The spelling of 21505071 in words is "twenty-one million, five hundred five thousand, seventy-one".