Find largest left truncatable prime in a given base: Difference between revisions
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I think I'll need to find a faster computer to calculate much more of the sequence, but memory consumption is currently negligible so there's no reason to expect there to be any major problems. |
I think I'll need to find a faster computer to calculate much more of the sequence, but memory consumption is currently negligible so there's no reason to expect there to be any major problems. |
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=={{header|zkl}}== |
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<lang zkl>var [const] BN=Import("zklBigNum"); // libGMP |
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fcn largest_lefty_prime(base){ |
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primes,p:=List(),BN(1); while(p.nextPrime()<base){ primes.append(p.copy()) } |
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b,biggest := BN(1),0; |
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while(primes){ |
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b.mul(base); // base,base^2,base^3... |
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ps:=List(); |
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foreach p,n in (primes,[1..base-1]){ |
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if((z:=(p + b*n)).probablyPrime()){ |
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ps.append(z); |
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if(biggest<z) biggest=z; |
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} |
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} |
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primes=ps; // the number of lists is small |
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} |
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biggest |
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} |
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foreach n in ([3..17]){ println("%2d %s".fmt(n,largest_lefty_prime(n))) }</lang> |
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I've included 18,19 & 20 here but 18 & 20 are very very slow to compute, it is seconds to compute all the others. |
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{{out}} |
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<pre> |
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3 23 |
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4 4091 |
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5 7817 |
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6 4836525320399 |
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7 817337 |
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8 14005650767869 |
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9 1676456897 |
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10 357686312646216567629137 |
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11 2276005673 |
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12 13092430647736190817303130065827539 |
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13 812751503 |
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14 615419590422100474355767356763 |
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15 34068645705927662447286191 |
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16 1088303707153521644968345559987 |
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17 13563641583101 |
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18 571933398724668544269594979167602382822769202133808087 |
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19 546207129080421139 |
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20 1073289911449776273800623217566610940096241078373 |
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</pre> |
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