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A044631
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Numbers n such that string 7,7 occurs in the base 8 representation of n but not of n+1.
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1
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63, 127, 191, 255, 319, 383, 447, 511, 575, 639, 703, 767, 831, 895, 959, 1023, 1087, 1151, 1215, 1279, 1343, 1407, 1471, 1535, 1599, 1663, 1727, 1791, 1855, 1919, 1983, 2047, 2111, 2175, 2239, 2303, 2367, 2431, 2495, 2559, 2623, 2687, 2751, 2815, 2879, 2943
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OFFSET
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1,1
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LINKS
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MATHEMATICA
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f[n_] := Length[StringPosition[ToString[FromDigits[IntegerDigits[n, 8]]], "77", 1]]; a1 = Select[Table[n, {n, 10000}], f[#] > 0 && f[# + 1] == 0 &] (* Vladimir Joseph Stephan Orlovsky, Jul 14 2011 *)
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PROG
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(PARI) has77(n)=my(t); while(n, if(bitand(n, 7)==7, if(t, return(1), t=1), t=0); n>>=3); 0
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CROSSREFS
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KEYWORD
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nonn,base
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AUTHOR
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STATUS
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approved
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