21620509 has 2 divisors, whose sum is σ = 21620510. Its totient is φ = 21620508.

The previous prime is 21620507. The next prime is 21620513. The reversal of 21620509 is 90502612.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 12602500 + 9018009 = 3550^2 + 3003^2 .

It is a cyclic number.

It is not a de Polignac number, because 21620509 - 2¹ = 21620507 is a prime.

Together with 21620507, it forms a pair of twin primes.

It is a plaindrome in base 11.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21620507) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10810254 + 10810255.

It is an arithmetic number, because the mean of its divisors is an integer number (10810255).

Almost surely, 2^21620509 is an apocalyptic number.

It is an amenable number.

21620509 is a deficient number, since it is larger than the sum of its proper divisors (1).

21620509 is an equidigital number, since it uses as much as digits as its factorization.

21620509 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1080, while the sum is 25.

The square root of 21620509 is about 4649.7859090500. The cubic root of 21620509 is about 278.5834450469.

The spelling of 21620509 in words is "twenty-one million, six hundred twenty thousand, five hundred nine".