21420181 has 4 divisors (see below), whose sum is σ = 21632364. Its totient is φ = 21208000.

The previous prime is 21420169. The next prime is 21420209. The reversal of 21420181 is 18102412.

It is a happy number.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 9205156 + 12215025 = 3034^2 + 3495^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21420181 is a prime.

It is a super-2 number, since 2×21420181² = 917648308145522, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21420121) 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, 105940 + ... + 106141.

It is an arithmetic number, because the mean of its divisors is an integer number (5408091).

Almost surely, 2^21420181 is an apocalyptic number.

It is an amenable number.

21420181 is a deficient number, since it is larger than the sum of its proper divisors (212183).

21420181 is a wasteful number, since it uses less digits than its factorization.

21420181 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 212182.

The product of its (nonzero) digits is 128, while the sum is 19.

The square root of 21420181 is about 4628.1941402668. The cubic root of 21420181 is about 277.7203552355.

Adding to 21420181 its reverse (18102412), we get a palindrome (39522593).

The spelling of 21420181 in words is "twenty-one million, four hundred twenty thousand, one hundred eighty-one".