661 is a Prime Number, Prime(121)
661 = 123 + 4 + 5 × 6 + 7 × 8 × 9
661 = 9 + 8 × 76 + 5 × 4 + 3 + 21
661 = 0^5 + 1^7 + 2^8 − 3^9 + 4^2 + 5^6 + 6^1 + 7^3 + 8^4 + 9^0
661 = 6^2 + 25^2
661^2 = 300^2 + 589^2
661 divides 9^11 - 1.
Prime of the form 2x^2 + 13y^2.
Prime of form x^2+29*y^2.
Prime p such that (p+1)/2 is prime.
Centered 12-gonal number, or centered dodecagonal number: number of the form 6*k*(k-1) + 1.
Factors: 1, 661
Six hundred sixty-one
Representations, Binary to Hexadecimal:
1010010101_2
220111_3
22111_4
10121_5
3021_6
1633_7
1225_8
814_9
551_11
471_12
3bb_13
353_14
2e1_15
295_16
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