21031313 has 2 divisors, whose sum is σ = 21031314. Its totient is φ = 21031312.

The previous prime is 21031303. The next prime is 21031333. The reversal of 21031313 is 31313012.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20502784 + 528529 = 4528^2 + 727^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21031313 is a prime.

It is a super-2 number, since 2×21031313² = 884632253007938, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21031303) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10515656 + 10515657.

It is an arithmetic number, because the mean of its divisors is an integer number (10515657).

Almost surely, 2^21031313 is an apocalyptic number.

It is an amenable number.

21031313 is a deficient number, since it is larger than the sum of its proper divisors (1).

21031313 is an equidigital number, since it uses as much as digits as its factorization.

21031313 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 54, while the sum is 14.

The square root of 21031313 is about 4585.9909507107. The cubic root of 21031313 is about 276.0294768280.

Adding to 21031313 its reverse (31313012), we get a palindrome (52344325).

The spelling of 21031313 in words is "twenty-one million, thirty-one thousand, three hundred thirteen".