561

561 = 3 × 11 × 17

561 = 1 + 2 + 3 + 45 + 6 + 7 × 8 × 9

561 = 9 + 87 × 6 + 5 + 4 × 3 × 2 + 1

561 = 0^4 − 1^7 − 2^9 − 3^8 + 4^6 + 5^5 + 6^1 + 7^3 + 8^2 + 960

Number k such that k^2 + 2 is prime

Carmichael number: composite numbers k such that a^(k-1) == 1 (mod k) for every a coprime to k.

Centered icosahedral (or cuboctahedral) number, also crystal ball sequence for f.c.c. lattice.

Sphenic number: Product of 3 distinct Primes, (List)

Factors: 1, 3, 11, 17, 33, 51, 187, 561

Representations, Binary to Hexadecimal:

1000110001_2
202210_3
20301_4
4221_5
2333_6
1431_7
1061_8
683_9
470_11
3a9_12
342_13
2c1_14
276_15
231_16

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