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A044631 Numbers n such that string 7,7 occurs in the base 8 representation of n but not of n+1. 1
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 1..1000

Tanya Khovanova, Non Recursions

MATHEMATICA

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 *)

PROG

(PARI) has77(n)=my(t); while(n, if(bitand(n, 7)==7, if(t, return(1), t=1), t=0); n>>=3); 0

is(n)=has77(n)&&!has77(n+1) \\ Charles R Greathouse IV, Jul 14 2011

CROSSREFS

Sequence in context: A043450 A031491 A044250 * A045136 A031895 A044314

Adjacent sequences:  A044628 A044629 A044630 * A044632 A044633 A044634

KEYWORD

nonn,base

AUTHOR

Clark Kimberling

STATUS

approved

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Last modified September 26 10:46 EDT 2017. Contains 292518 sequences.