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A081939 a(1) = 2; a(n+1) is the smallest palindrome > a(n) that has a common factor with a(n). 4
2, 4, 6, 8, 22, 33, 44, 55, 66, 77, 88, 99, 111, 141, 171, 222, 232, 242, 252, 262, 272, 282, 292, 404, 414, 424, 434, 444, 454, 464, 474, 484, 494, 585, 595, 616, 626, 636, 646, 656, 666, 676, 686, 696, 717, 747, 777, 828, 838, 848, 858, 868, 878, 888, 898 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Palindromes with an even number of digits are divisible by 11, so when a(n)=A002113(k) and A055642(a(n)) and A055642(A002113(k+1)) are even, a(n+1)=A002113(k+1). - Robert Israel, Jul 04 2018

LINKS

Robert Israel, Table of n, a(n) for n = 1..10000

Index entries for sequences related to palindromes

MAPLE

dmax:= 5: # to get all terms with at most dmax digits

revdigs:= proc(n)

  local L, Ln, i;

  L:= convert(n, base, 10);

  Ln:= nops(L);

  add(L[i]*10^(Ln-i), i=1..Ln);

end proc:

P:= $0..9:

for d from 2 to dmax do

  if d::even then

    P:= P, seq(10^(d/2)*x + revdigs(x), x=10^(d/2-1)..10^(d/2)-1)

  else

    m:= (d-1)/2;

    P:= P, seq(seq(10^(m+1)*x + 10^m*j+revdigs(x), j=0..9), x=10^(m-1)..10^m-1);

  fi

od:

P:= [P]:

r:= P[3]: Res:= r: count:= 1:

for i from 4 to nops(P) do

  if igcd(P[i], r) > 1 then

    count:= count+1; r:= P[i]; Res:= Res, r;

  fi

od:

Res; # Robert Israel, Jul 04 2018

PROG

(PARI) ispal(n) = my(d=digits(n)); d == Vecrev(d);

lista(nn) = {print1(last = 2, ", "); for (n=3, nn, if (ispal(n) && (gcd(n, last) != 1), print1(n, ", "); last = n; ); ); } \\ Michel Marcus, Aug 12 2015

CROSSREFS

Cf. A002113, A055642, A083136, A081938.

Sequence in context: A045927 A165931 A321600 * A082615 A277258 A029951

Adjacent sequences:  A081936 A081937 A081938 * A081940 A081941 A081942

KEYWORD

base,nonn

AUTHOR

Amarnath Murthy, Apr 02 2003

EXTENSIONS

More terms from David Wasserman, Jun 29 2004

STATUS

approved

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Last modified May 20 20:16 EDT 2019. Contains 323426 sequences. (Running on oeis4.)