21212431 has 2 divisors, whose sum is σ = 21212432. Its totient is φ = 21212430.

The previous prime is 21212423. The next prime is 21212449. The reversal of 21212431 is 13421212.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21212431 - 2³ = 21212423 is a prime.

It is a super-2 number, since 2×21212431² = 899934457859522, which contains 22 as substring.

It is equal to p_1342510 and since 21212431 and 1342510 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 (21212461) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10606215 + 10606216.

It is an arithmetic number, because the mean of its divisors is an integer number (10606216).

Almost surely, 2^21212431 is an apocalyptic number.

21212431 is a deficient number, since it is larger than the sum of its proper divisors (1).

21212431 is an equidigital number, since it uses as much as digits as its factorization.

21212431 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 96, while the sum is 16.

The square root of 21212431 is about 4605.6954957965. The cubic root of 21212431 is about 276.8195856298.

Adding to 21212431 its reverse (13421212), we get a palindrome (34633643).

The spelling of 21212431 in words is "twenty-one million, two hundred twelve thousand, four hundred thirty-one".