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A072431 Numbers n for which there are exactly seven k such that n = k + reverse(k).

%I A072431 #13 Aug 11 2014 22:45:22
%S A072431 77,132,707,727,747,767,787,807,827,847,867,887,1212,1232,1252,1272,
%T A072431 1292,1312,1332,1352,1372,1392,1661,2321,7007,8987,12012,13992,16061,
%U A072431 16261,16461,16661,16861,17061,17261,17461,17661,17861,18678,19338
%N A072431 Numbers n for which there are exactly seven k such that n = k + reverse(k).
%C A072431 Subsequence of A067030. First term is A072041(7).
%H A072431 T. D. Noe, <a href="/A072431/b072431.txt">Table of n, a(n) for n = 1..254</a>
%H A072431 <a href="/index/Res#RAA">Index entries for sequences related to Reverse and Add!</a>
%e A072431 77 = k + reverse(k) for k = 16, 25, 34, 43, 52, 61, 70; 132 = k + reverse(k) for k = 39, 48, 57, 66, 75, 84, 93.
%t A072431 f[n_] := n + FromDigits@ Reverse@ IntegerDigits@ n; fQ[n_] := Block[{c = 0, k = 1}, While[k < n && n != f@ k, k++]; While[k < n, If[n == f@ k, c++]; k += 9]; c == 7]; Select[ Range@ 20000, fQ]
%t A072431 revAdd[n_] := n + FromDigits[Reverse[IntegerDigits[n]]]; ra=Table[revAdd[n], {n, 0, 10^5}]; t=Sort[Tally[ra]]; First /@ Select[t, #[[2]] == 7 && #[[1]] < Length[ra] &]
%o A072431 (ARIBAS) var n,k,c,i,rev: integer; st,nst: string; end; m := 7; for n := 0 to 22600 do k := n div 2; c := 0; while k <= n and c < m + 1 do st := itoa(k); nst := ""; for i := 0 to length(st) - 1 do nst := concat(st[i],nst); end; rev := atoi(nst); if n = k + rev then inc(c); if k mod 10 <> 0 and k <> rev then inc(c); end; end; inc(k); end; if c = m then write(n,","); end; end;
%Y A072431 Cf. A067030, A072041.
%K A072431 base,nonn
%O A072431 1,1
%A A072431 _Klaus Brockhaus_, Jun 17 2002