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A215797
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Numbers n such that n(n+1)/2 + 1 is a power of 2.
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3
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OFFSET
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1,3
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COMMENTS
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No other terms < 10^6. - T. D. Noe, Aug 25 2012
This sequence maps to the Ramanujan-Nagell squares (8*(n*(n+1)/2)+1) and is therefore complete. - Raphie Frank, Aug 26 2012
All terms in this sequence follow form floor[2^((2*x - 1)/2)]; x = {0, 1, 2, 3, 7}. - Raphie Frank, Mar 03 2013
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LINKS
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FORMULA
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MATHEMATICA
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Select[Range[0, 1000], IntegerQ[Log[2, 1 + #(#+1)/2]]&] (* T. D. Noe, Aug 25 2012 *)
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PROG
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(PARI) for(n=0, 100, if(ispolygonal(2^n-1, 3), print1(sqrtint(2*2^n-2)", "))) \\ Charles R Greathouse IV, Mar 04 2013
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CROSSREFS
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Cf. A060728, A038198 (two references to the Ramanujan-Nagell problem).
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KEYWORD
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nonn,fini,full
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AUTHOR
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STATUS
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approved
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