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
KEYWORD
nonn,base
AUTHOR
STATUS
approved