21555461 has 2 divisors, whose sum is σ = 21555462. Its totient is φ = 21555460.

The previous prime is 21555451. The next prime is 21555467. The reversal of 21555461 is 16455512.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21390625 + 164836 = 4625^2 + 406^2 .

It is a cyclic number.

It is not a de Polignac number, because 21555461 - 2¹⁸ = 21293317 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21555467) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10777730 + 10777731.

It is an arithmetic number, because the mean of its divisors is an integer number (10777731).

Almost surely, 2^21555461 is an apocalyptic number.

It is an amenable number.

21555461 is a deficient number, since it is larger than the sum of its proper divisors (1).

21555461 is an equidigital number, since it uses as much as digits as its factorization.

21555461 is an evil number, because the sum of its binary digits is even.

The product of its digits is 6000, while the sum is 29.

The square root of 21555461 is about 4642.7859093437. The cubic root of 21555461 is about 278.3037800343.

The spelling of 21555461 in words is "twenty-one million, five hundred fifty-five thousand, four hundred sixty-one".