A069881 Numbers n such that n and 2n+1 are both palindromes.
1, 2, 3, 4, 5, 55, 151, 161, 171, 181, 191, 252, 262, 272, 282, 292, 353, 363, 373, 383, 393, 454, 464, 474, 484, 494, 555, 5555, 15051, 15151, 15251, 15351, 15451, 16061, 16161, 16261, 16361, 16461, 17071, 17171, 17271, 17371, 17471, 18081, 18181
Offset: 1
Examples
151 is a member as 2*151 + 1 = 303 is also a palindrome.
Links
- Ivan Neretin, Table of n, a(n) for n = 1..15636 (all terms up to 10^12)
Crossrefs
Subsequence of A002113.
Programs
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Mathematica
isPalin[n_]:=(n==FromDigits[Reverse[IntegerDigits[n]]]); Do[m = 2 n + 1; If[isPalin[n]&&isPalin[m], Print[n]], {n, 1, 10^5}] (* Vincenzo Librandi, Jan 22 2018 *) -
PARI
isok(n) = (d=digits(n)) && (Vecrev(d)==d) && (dd=digits(2*n+1)) && (Vecrev(dd)==dd); \\ Michel Marcus, Jan 22 2018
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Perl
$a = 1; while((@b = split("|",$a) and @c = split("|",2*$a+1) and (join("", reverse(@b)) eq join("", @b) and join("", reverse(@c)) eq join("", @c) and eval("print \"\$a \"; return 0;"))) or ++$a) { }
Extensions
More terms from Jim McCann (jmccann(AT)umich.edu), Jul 16 2002
Comments