21501281 has 2 divisors, whose sum is σ = 21501282. Its totient is φ = 21501280.

The previous prime is 21501253. The next prime is 21501287. The reversal of 21501281 is 18210512.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 15171025 + 6330256 = 3895^2 + 2516^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21501281 is a prime.

It is a super-2 number, since 2×21501281² = 924610169281922, which contains 22 as substring.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21501287) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10750640 + 10750641.

It is an arithmetic number, because the mean of its divisors is an integer number (10750641).

Almost surely, 2^21501281 is an apocalyptic number.

It is an amenable number.

21501281 is a deficient number, since it is larger than the sum of its proper divisors (1).

21501281 is an equidigital number, since it uses as much as digits as its factorization.

21501281 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 160, while the sum is 20.

The square root of 21501281 is about 4636.9473794728. The cubic root of 21501281 is about 278.0704107144.

Adding to 21501281 its reverse (18210512), we get a palindrome (39711793).

The spelling of 21501281 in words is "twenty-one million, five hundred one thousand, two hundred eighty-one".