21003121 has 2 divisors, whose sum is σ = 21003122. Its totient is φ = 21003120.

The previous prime is 21003107. The next prime is 21003139. The reversal of 21003121 is 12130012.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 15054400 + 5948721 = 3880^2 + 2439^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21003121 is a prime.

It is a super-2 number, since 2×21003121² = 882262183481282, which contains 22 as substring.

It is a Chen prime.

It is a junction number, because it is equal to n+sod(n) for n = 21003098 and 21003107.

It is not a weakly prime, because it can be changed into another prime (21003821) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10501560 + 10501561.

It is an arithmetic number, because the mean of its divisors is an integer number (10501561).

Almost surely, 2^21003121 is an apocalyptic number.

It is an amenable number.

21003121 is a deficient number, since it is larger than the sum of its proper divisors (1).

21003121 is an equidigital number, since it uses as much as digits as its factorization.

21003121 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 12, while the sum is 10.

The square root of 21003121 is about 4582.9162113222. The cubic root of 21003121 is about 275.9060845839.

Adding to 21003121 its reverse (12130012), we get a palindrome (33133133).

The spelling of 21003121 in words is "twenty-one million, three thousand, one hundred twenty-one".