21181669 has 2 divisors, whose sum is σ = 21181670. Its totient is φ = 21181668.

The previous prime is 21181663. The next prime is 21181673. The reversal of 21181669 is 96618112.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21068100 + 113569 = 4590^2 + 337^2 .

It is a cyclic number.

It is not a de Polignac number, because 21181669 - 2⁹ = 21181157 is a prime.

It is a super-2 number, since 2×21181669² = 897326203251122, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21181663) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10590834 + 10590835.

It is an arithmetic number, because the mean of its divisors is an integer number (10590835).

Almost surely, 2^21181669 is an apocalyptic number.

It is an amenable number.

21181669 is a deficient number, since it is larger than the sum of its proper divisors (1).

21181669 is an equidigital number, since it uses as much as digits as its factorization.

21181669 is an evil number, because the sum of its binary digits is even.

The product of its digits is 5184, while the sum is 34.

The square root of 21181669 is about 4602.3547233998. The cubic root of 21181669 is about 276.6857074684.

The spelling of 21181669 in words is "twenty-one million, one hundred eighty-one thousand, six hundred sixty-nine".