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

Offset: 1

Author

Klaus Brockhaus, Jun 08 2002

Keywords

• base
• nonn

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.

Examples

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

Links

• Index entries for sequences related to Reverse and Add!

Crossrefs

Cf. A067030, A071265, A072041, A096768.

Programs

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[A072040%20=%20Reap%5BFor%5Bn%20=%201,%20n%20%3C=%20M,%20n++,%20If%5Bb%5Bn%5D%20==%202,%20Sow%5Bn%5D%5D%5D%5D%5B%5B2,%201%5D%5D%20(*%20_Jean-Fran%C3%A7ois%20Alcover">] = 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 *)