1561221461 has 2 divisors, whose sum is σ = 1561221462. Its totient is φ = 1561221460.

The previous prime is 1561221457. The next prime is 1561221551. The reversal of 1561221461 is 1641221651.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1324523236 + 236698225 = 36394^2 + 15385^2 .

It is an emirp because it is prime and its reverse (1641221651) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 1561221461 - 2² = 1561221457 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1561226461) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 780610730 + 780610731.

It is an arithmetic number, because the mean of its divisors is an integer number (780610731).

Almost surely, 2^1561221461 is an apocalyptic number.

It is an amenable number.

1561221461 is a deficient number, since it is larger than the sum of its proper divisors (1).

1561221461 is an equidigital number, since it uses as much as digits as its factorization.

1561221461 is an evil number, because the sum of its binary digits is even.

The product of its digits is 2880, while the sum is 29.

The square root of 1561221461 is about 39512.2950611579. The cubic root of 1561221461 is about 1160.0806179107.

It can be divided in two parts, 15612 and 21461, that added together give a palindrome (37073).

The spelling of 1561221461 in words is "one billion, five hundred sixty-one million, two hundred twenty-one thousand, four hundred sixty-one".