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Numbers k such that 4 and 7 occur juxtaposed in the base-10 representation of k but not of k+1.

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`%I #12 Aug 29 2021 01:55:35
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`%S 47,74,147,174,247,274,347,374,447,479,547,574,647,674,749,774,847,
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`%T 874,947,974,1047,1074,1147,1174,1247,1274,1347,1374,1447,1479,1547,
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`%U 1574,1647,1674,1749,1774,1847,1874,1947,1974,2047
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`%N Numbers k such that 4 and 7 occur juxtaposed in the base-10 representation of k but not of k+1.
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`%t okQ[n_]:=Module[{sidn=Sort/@Partition[IntegerDigits[n],2,1]},MemberQ[sidn,{4,7}]]; Select[Range[2100],okQ[#]&&!okQ[#+1]&] (* _Harvey P. Dale_, Feb 14 2012 *)
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`%K nonn,base
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`%O 1,1
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`%A _Clark Kimberling_
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