21506417 has 2 divisors, whose sum is σ = 21506418. Its totient is φ = 21506416.

The previous prime is 21506389. The next prime is 21506431. The reversal of 21506417 is 71460512.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 14318656 + 7187761 = 3784^2 + 2681^2 .

It is a cyclic number.

It is not a de Polignac number, because 21506417 - 2¹⁴ = 21490033 is a prime.

It is not a weakly prime, because it can be changed into another prime (21506437) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10753208 + 10753209.

It is an arithmetic number, because the mean of its divisors is an integer number (10753209).

Almost surely, 2^21506417 is an apocalyptic number.

It is an amenable number.

21506417 is a deficient number, since it is larger than the sum of its proper divisors (1).

21506417 is an equidigital number, since it uses as much as digits as its factorization.

21506417 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1680, while the sum is 26.

The square root of 21506417 is about 4637.5011590295. The cubic root of 21506417 is about 278.0925497973.

Adding to 21506417 its reverse (71460512), we get a palindrome (92966929).

The spelling of 21506417 in words is "twenty-one million, five hundred six thousand, four hundred seventeen".