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A213879 Positive palindromes that are not the sum of two positive palindromes. 6
1, 111, 131, 141, 151, 161, 171, 181, 191, 1331, 1441, 1551, 1661, 1771, 1881, 1991, 10301, 10401, 10501, 10601, 10701, 10801, 10901, 11111, 11211, 11311, 11411, 11511, 11611, 11711, 11811, 11911, 12021, 12121, 12321, 12421, 12521, 12621, 12721, 12821 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

These numbers do not occur in A035137.

LINKS

Alois P. Heinz, Table of n, a(n) for n = 1..2151 (first 111 terms from N. J. A. Sloane)

Eric Weisstein's World of Mathematics, Palindromic Number

Index entries for sequences related to palindromes

FORMULA

({ A002113 } intersect { A319477 }) minus { 0 }. - Alois P. Heinz, Sep 19 2018

EXAMPLE

22 is not a member because 22 = 11 + 11.

MAPLE

# From N. J. A. Sloane, Sep 09 2015: bP is a list of the palindromes

a:={}; M:=400; for n from 3 to M do p:=bP[n];

# is p a sum of two palindromes?

sw:=-1; for i from 2 to n-1 do j:=p-bP[i]; if digrev(j)=j then sw:=1; break; fi;

od;

if sw<0 then a:={op(a), p}; fi; od:

b:=sort(convert(a, list));

MATHEMATICA

lst1 = {}; lst2 = {}; r = 12821; Do[If[FromDigits@Reverse@IntegerDigits[n] == n, AppendTo[lst1, n]], {n, r}]; l = Length[lst1]; Do[s = lst1[[i]] + lst1[[j]]; AppendTo[lst2, s], {i, l - 1}, {j, i}]; Complement[lst1, lst2]

palQ[n_] := Reverse[x = IntegerDigits[n]] == x; t1 = Select[Range[12900], palQ[#] &]; Complement[t1, Union[Flatten[Table[i + j, {i, t1}, {j, t1}]]]] (* Jayanta Basu, Jun 15 2013 *)

CROSSREFS

Cf. A002113, A014092, A035137, A083142, A088601, A260255, A319477.

Sequence in context: A070798 A235039 A279423 * A095613 A108721 A084325

Adjacent sequences:  A213876 A213877 A213878 * A213880 A213881 A213882

KEYWORD

base,nonn

AUTHOR

Arkadiusz Wesolowski, Jun 23 2012

STATUS

approved

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Last modified April 5 16:04 EDT 2020. Contains 333245 sequences. (Running on oeis4.)