21691481 has 4 divisors (see below), whose sum is σ = 24790272. Its totient is φ = 18592692.

The previous prime is 21691459. The next prime is 21691489. The reversal of 21691481 is 18419612.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21691481 - 2²² = 17497177 is a prime.

It is a super-2 number, since 2×21691481² = 941040695946722, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21691489) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1549385 + ... + 1549398.

It is an arithmetic number, because the mean of its divisors is an integer number (6197568).

Almost surely, 2^21691481 is an apocalyptic number.

It is an amenable number.

21691481 is a deficient number, since it is larger than the sum of its proper divisors (3098791).

21691481 is an equidigital number, since it uses as much as digits as its factorization.

21691481 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3098790.

The product of its digits is 3456, while the sum is 32.

The square root of 21691481 is about 4657.4114054913. The cubic root of 21691481 is about 278.8879403352.

The spelling of 21691481 in words is "twenty-one million, six hundred ninety-one thousand, four hundred eighty-one".