21505491 has 12 divisors (see below), whose sum is σ = 35501232. Its totient is φ = 12288816.

The previous prime is 21505481. The next prime is 21505499. The reversal of 21505491 is 19450512.

It is not a de Polignac number, because 21505491 - 2¹⁵ = 21472723 is a prime.

It is a super-2 number, since 2×21505491² = 924972286302162, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21505499) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 170616 + ... + 170741.

It is an arithmetic number, because the mean of its divisors is an integer number (2958436).

Almost surely, 2^21505491 is an apocalyptic number.

21505491 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

21505491 is a deficient number, since it is larger than the sum of its proper divisors (13995741).

21505491 is a wasteful number, since it uses less digits than its factorization.

21505491 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 341370 (or 341367 counting only the distinct ones).

The product of its (nonzero) digits is 1800, while the sum is 27.

The square root of 21505491 is about 4637.4013197048. The cubic root of 21505491 is about 278.0885584708.

The spelling of 21505491 in words is "twenty-one million, five hundred five thousand, four hundred ninety-one".