21500261 has 2 divisors, whose sum is σ = 21500262. Its totient is φ = 21500260.

The previous prime is 21500251. The next prime is 21500273. The reversal of 21500261 is 16200512.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 16048036 + 5452225 = 4006^2 + 2335^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21500261 is a prime.

It is a super-2 number, since 2×21500261² = 924522446136242, which contains 22 as substring.

It is a Sophie Germain prime.

It is a Chen prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21500231) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10750130 + 10750131.

It is an arithmetic number, because the mean of its divisors is an integer number (10750131).

Almost surely, 2^21500261 is an apocalyptic number.

It is an amenable number.

21500261 is a deficient number, since it is larger than the sum of its proper divisors (1).

21500261 is an equidigital number, since it uses as much as digits as its factorization.

21500261 is an odious number, because the sum of its binary digits is odd.

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

The square root of 21500261 is about 4636.8373920162. The cubic root of 21500261 is about 278.0660135143.

Adding to 21500261 its reverse (16200512), we get a palindrome (37700773).

The spelling of 21500261 in words is "twenty-one million, five hundred thousand, two hundred sixty-one".