1. Express the number in base 27:
n=1⋅2725+2⋅2724+3⋅2723+…+25⋅27+26
2. Rewrite the sum:
n=(2725+2724+…+27+1)+(2724+2723+…+27+1)+…+(27+1)+1
3. Use the geometric series formula:
Each term in the sum can be expressed using the geometric series formula:
k=0∑m27k=2627m+1−1
Applying this to each term, we get:
n=262726−1+262725−1+262724−1+…+26272−1+2627−1
4. Combine the terms:
26n=2726+2725+2724+…+272+27−26
5. Use the geometric series formula again:
26n=262727−1−27
Simplifying, we get:
26n=262727−703
Multiplying both sides by 26:
676n=2727−703
6. Simplify using modular arithmetic:
Since λ(100)=20 (Carmichael function), we have:
381≡3mod100
Therefore:
2727≡381≡3mod100
Thus:
676n≡3−703≡3−703≡−700≡0mod100
7. **Determine possible values of nmod100:**
Since 676n≡0mod100 and gcd(676,100)=4, we have:
676n≡0mod100⟹n≡0,25,50,75mod100
8. Use modulo 4 to narrow down the options:
n≡(2+4+6+…+26)+3(1+3+5+…+25)mod4
The sum of the first series is:
2(1+2+3+…+13)=2⋅213⋅14=13⋅14≡1mod4
The sum of the second series is:
3(1+3+5+…+25)=3⋅132=3⋅169≡3⋅1=3mod4
Therefore:
n≡1+3=4≡0mod4
This eliminates 25, 50, and 75, leaving:
n≡0mod100
The final answer is 0