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Search: id:A103788
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| 0, 1, 3, 6, 13, 28, 39, 78, 138, 207, 437, 865, 1423, 2750, 4904, 8861, 16201, 33346, 58534, 111878, 208914, 397522
(list; graph; listen)
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OFFSET
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1,3
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EXAMPLE
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P(2)/A(0)-A(0)=6-1=5 is prime, so a(2)=1;
P(4)/A(k)-A(k): 210/2-2=103; 210/3-3=67; 210/6-6=29; 210/5-5=37; 210/10-10=11; 210/7-7=23; so a(4)=6;
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MATHEMATICA
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npd = 1; Do[npd = npd*Prime[n]; tn = 0; tt = 1; cp = npd/tt - tt; ct = 0; While[IntegerQ[cp], If[(cp > 0) && PrimeQ[cp], ct = ct + 1]; tn = tn + 1; tt = 1; k1 = tn; o = 1; While[k1 > 0, k2 = Mod[k1, 2]; If[k2 == 1, tt = tt*Prime[o]]; k1 = ( k1 - k2)/2; o = o + 1]; cp = npd/tt - tt]; Print[ct], {n, 1, 22}]
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CROSSREFS
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Cf. A019565, A002110, A103785, A103786, A103787.
Sequence in context: A052251 A032253 A125777 this_sequence A106461 A095768 A002478
Adjacent sequences: A103785 A103786 A103787 this_sequence A103789 A103790 A103791
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KEYWORD
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hard,nonn
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AUTHOR
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Lei Zhou (lzhou5(AT)emory.edu), Feb 16 2005
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