21455261 has 2 divisors, whose sum is σ = 21455262. Its totient is φ = 21455260.

The previous prime is 21455257. The next prime is 21455263. The reversal of 21455261 is 16255412.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 15452761 + 6002500 = 3931^2 + 2450^2 .

It is a cyclic number.

It is not a de Polignac number, because 21455261 - 2² = 21455257 is a prime.

Together with 21455263, it forms a pair of twin primes.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21455261.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21455263) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10727630 + 10727631.

It is an arithmetic number, because the mean of its divisors is an integer number (10727631).

Almost surely, 2^21455261 is an apocalyptic number.

It is an amenable number.

21455261 is a deficient number, since it is larger than the sum of its proper divisors (1).

21455261 is an equidigital number, since it uses as much as digits as its factorization.

21455261 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 2400, while the sum is 26.

The square root of 21455261 is about 4631.9824049752. The cubic root of 21455261 is about 277.8718808222.

The spelling of 21455261 in words is "twenty-one million, four hundred fifty-five thousand, two hundred sixty-one".