21266551 has 2 divisors, whose sum is σ = 21266552. Its totient is φ = 21266550.

The previous prime is 21266521. The next prime is 21266561. The reversal of 21266551 is 15566212.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21266551 - 2⁵ = 21266519 is a prime.

It is equal to p_1345717 and since 21266551 and 1345717 have the same sum of digits, it is a Honaker prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21266521) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10633275 + 10633276.

It is an arithmetic number, because the mean of its divisors is an integer number (10633276).

Almost surely, 2^21266551 is an apocalyptic number.

21266551 is a deficient number, since it is larger than the sum of its proper divisors (1).

21266551 is an equidigital number, since it uses as much as digits as its factorization.

21266551 is an evil number, because the sum of its binary digits is even.

The product of its digits is 3600, while the sum is 28.

The square root of 21266551 is about 4611.5670872275. The cubic root of 21266551 is about 277.0548054574.

The spelling of 21266551 in words is "twenty-one million, two hundred sixty-six thousand, five hundred fifty-one".