21272681 has 2 divisors, whose sum is σ = 21272682. Its totient is φ = 21272680.

The previous prime is 21272621. The next prime is 21272683. The reversal of 21272681 is 18627212.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 16362025 + 4910656 = 4045^2 + 2216^2 .

It is a cyclic number.

It is not a de Polignac number, because 21272681 - 2⁶ = 21272617 is a prime.

It is a super-2 number, since 2×21272681² = 905053913855522, which contains 22 as substring.

Together with 21272683, it forms a pair of twin primes.

It is a Chen prime.

It is equal to p_1346087 and since 21272681 and 1346087 have the same sum of digits, it is a Honaker prime.

It is not a weakly prime, because it can be changed into another prime (21272683) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10636340 + 10636341.

It is an arithmetic number, because the mean of its divisors is an integer number (10636341).

Almost surely, 2^21272681 is an apocalyptic number.

It is an amenable number.

21272681 is a deficient number, since it is larger than the sum of its proper divisors (1).

21272681 is an equidigital number, since it uses as much as digits as its factorization.

21272681 is an evil number, because the sum of its binary digits is even.

The product of its digits is 2688, while the sum is 29.

The square root of 21272681 is about 4612.2316724120. The cubic root of 21272681 is about 277.0814228874.

Adding to 21272681 its reverse (18627212), we get a palindrome (39899893).

The spelling of 21272681 in words is "twenty-one million, two hundred seventy-two thousand, six hundred eighty-one".