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Search: id:A100348
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| A100348 |
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Numbers n such that n-4^k is a prime for all k > 0 with 4^k < n. |
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+0
2
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| 6, 7, 9, 11, 15, 21, 23, 27, 33, 35, 45, 47, 57, 63, 75, 77, 83, 87, 105, 117, 143, 153, 167, 195, 215, 227, 243, 245, 255, 287, 297, 413, 437, 447, 483, 495, 507, 525, 573, 635, 657, 677, 755, 825, 1113, 1133, 1295, 1487, 1515, 1547, 1617, 1623, 2015, 2043, 2397
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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The largest term appears to be 5833497. No others < 10^9; conjectured to be finite. Similar to A067528, which also contains 5 and 17, but a more direct generalization of A039669, a problem due to Erdos.
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EXAMPLE
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27 is here because 27-4 and 27-16 are primes.
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MATHEMATICA
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lst={}; Do[k=1; While[p=n-4^k; p>0 && PrimeQ[p], k++ ]; If[p<=0, AppendTo[lst, n]], {n, 5, 10^7}]; lst
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CROSSREFS
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Cf. A039669 (n such that n-2^k is prime), A067528 (n such that n-4^k is prime or 1).
Adjacent sequences: A100345 A100346 A100347 this_sequence A100349 A100350 A100351
Sequence in context: A120164 A074898 A094010 this_sequence A094698 A095908 A096405
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KEYWORD
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nonn
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AUTHOR
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T. D. Noe (noe(AT)sspectra.com), Nov 18 2004
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