21105431 has 2 divisors, whose sum is σ = 21105432. Its totient is φ = 21105430.

The previous prime is 21105419. The next prime is 21105433. The reversal of 21105431 is 13450112.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21105431 - 2⁶ = 21105367 is a prime.

It is a super-3 number, since 3×21105431³ (a number of 23 digits) contains 333 as substring. Note that it is a super-d number also for d = 2.

Together with 21105433, it forms a pair of twin primes.

It is a Chen prime.

It is equal to p_1336211 and since 21105431 and 1336211 have the same sum of digits, it is a Honaker prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21105433) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10552715 + 10552716.

It is an arithmetic number, because the mean of its divisors is an integer number (10552716).

Almost surely, 2^21105431 is an apocalyptic number.

21105431 is a deficient number, since it is larger than the sum of its proper divisors (1).

21105431 is an equidigital number, since it uses as much as digits as its factorization.

21105431 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 120, while the sum is 17.

The square root of 21105431 is about 4594.0647579241. The cubic root of 21105431 is about 276.3533552643.

Adding to 21105431 its reverse (13450112), we get a palindrome (34555543).

The spelling of 21105431 in words is "twenty-one million, one hundred five thousand, four hundred thirty-one".