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A215795
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Numbers n such that 2^n-1 is a triangular number (A000217).
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5
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OFFSET
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1,3
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COMMENTS
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Aside from a(2), all terms are even. Probably complete; no more terms up to 10^6. - Charles R Greathouse IV, Sep 07 2012
This sequence maps to the Ramanujan-Nagell squares (8*(2^n - 1) + 1) and is therefore complete. - Raphie Frank, Sep 10 2012
Define equivalence classes on a specified real interval with respect to the symmetric transitive closure of R(x,y) = "x is an integer multiple of y". If any equivalence class is finite (the conditions for which are given in A328129), then a smallest equivalence class has cardinality 1, 2, 4 or 12. - Peter Munn, Jun 02 2021
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LINKS
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PROG
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CROSSREFS
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Cf. A076046 (triangular numbers of the form 2^n - 1).
Cf. A215797 ((sqrt(8*(2^n - 1)+1) - 1)/2).
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KEYWORD
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nonn,fini,full
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AUTHOR
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EXTENSIONS
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Four cross-references to the Ramanujan-Nagell problem added by Raphie Frank, Sep 10 2012
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STATUS
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approved
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