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A079672
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Numbers of the form (3^s+1)/(3^r+1) for s>1, 1<=r<=s-1.
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3
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7, 61, 73, 547, 4921, 703, 5905, 44287, 6481, 398581, 478297, 3587227, 512461, 58807, 32285041, 38742049, 530713, 290565367, 42521761, 2615088301, 373584043, 4780783, 3138105961, 23535794707, 43040161, 211822152361, 3472494301
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| (b^s+1) / (b^r+1) is an integer iff s/r is odd. - Jose Brox (tautocrona(AT)terra.es), Dec 27 2005
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FORMULA
| (3^s+1)/(3^r+1) when it belongs to N for s from 2 to infinity for r from 1 to s-1
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PROG
| (PARI) for(x=2, 26, for(y=1, x-1, if(Mod(2^x+1, 2^y+1), 0, print1((3^x+1)/(3^y+1)", ")))) (* The Mod(2^x+1, 2^y+1) is not a bug, since the exponents do not depend on what base are calculated *)
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CROSSREFS
| Cf. A079665, A079581, A079673.
Sequence in context: A156545 A157871 A043085 * A173880 A100698 A141952
Adjacent sequences: A079669 A079670 A079671 * A079673 A079674 A079675
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KEYWORD
| nonn
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AUTHOR
| Jose R. Brox (tautocrona(AT)terra.es), Jan 25 2003
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