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 A233089 Numbers n such that 2n-1 and 2n+1 divide 2^n-1. 1
 8, 128, 228, 648, 3240, 5976, 13160, 23760, 23940, 24840, 32768, 37224, 78540, 82800, 139248, 166716, 238368, 278520, 280368, 288360, 516528, 633420, 664668, 731808, 734448, 1145520, 1211100, 1377240, 1425816, 1484568, 1627640, 2055060, 2131080, 2292780 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Intersection of A081856 and A081858. Numbers n such that 4n^2-1 divides 2^n-1. - Charles R Greathouse IV, Dec 04 2013 LINKS Charles R Greathouse IV, Table of n, a(n) for n = 1..5000 EXAMPLE 2^8-1=255 is divisible by 2*8-1=15 and by 2*8+1=17. MATHEMATICA Select[Range[23*10^5], PowerMod[2, #, 2#+{1, -1}]=={1, 1}&] (* Harvey P. Dale, Dec 19 2014 *) PROG (PARI) isok(n) = !((2^n-1) % (2*n-1)) && !((2^n-1) % (2*n+1)); (PARI) is(n)=Mod(2, 4*n^2-1)^n==1 \\ Charles R Greathouse IV, Dec 04 2013 CROSSREFS Sequence in context: A034220 A034239 A171755 * A204194 A093586 A238651 Adjacent sequences:  A233086 A233087 A233088 * A233090 A233091 A233092 KEYWORD nonn AUTHOR Michel Marcus, Dec 04 2013 STATUS approved

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Last modified September 19 10:41 EDT 2020. Contains 337178 sequences. (Running on oeis4.)