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A072040

Numbers n of the form k + reverse(k) for exactly two k.

22, 187, 202, 222, 242, 262, 282, 302, 322, 342, 362, 382, 1717, 1737, 1757, 1777, 1797, 1817, 1837, 1857, 1877, 1897, 2002, 2871, 3982, 11211, 11411, 11611, 11811, 12011, 12211, 12411, 12611, 12811, 17017, 18128, 18997, 19888, 20002, 20202

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OFFSET

1,1

COMMENTS

In the cognate sequence A071265 two numbers a and b are counted only once, if n = a + b, a = reverse(b), b = reverse(a). Therefore 187 = 89 + 98 = 98 + 89 does not appear in A071265.

LINKS

Table of n, a(n) for n=1..40.

Index entries for sequences related to Reverse and Add!

EXAMPLE

22 = 11 + 11 = 20 + 02, 187 = 89 + 98 = 98 + 89, 382 = 191 + 191 = 290 + 092.

MAPLE

# Maple program from N. J. A. Sloane, Mar 07 2016. Assumes digrev (from the "transforms" file) is available:

M:=21000; b := Array(1..M, 0);

for n from 1 to M do

t1:=n+digrev(n);

if t1 <= M then b[t1]:=b[t1]+1; fi;

od:

ans:=[];

for n from 1 to M do

if b[n]=2 then ans:=[op(ans), n]; fi; od:

ans;

MATHEMATICA

M = 10^5; digrev[n_] := IntegerDigits[n] // Reverse // FromDigits; Clear[b]; b[_] = 0; For[n = 1, n <= M, n++, t1 = n + digrev[n]; If[t1 <= M, b[t1] = b[t1] + 1]]; A072040 = Reap[For[n = 1, n <= M, n++, If[b[n] == 2, Sow[n]]]][[2, 1]] (* Jean-François Alcover, Oct 01 2016, after N. J. A. Sloane's Maple code *)

CROSSREFS

Cf. A067030, A071265, A072041, A096768.

Sequence in context: A229367 A129126 A231749 * A022682 A107959 A200936

Adjacent sequences: A072037 A072038 A072039 * A072041 A072042 A072043

KEYWORD

base,nonn

AUTHOR

Klaus Brockhaus, Jun 08 2002

STATUS

approved