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A030678 Smallest nontrivial extension of n-th palindrome which is a cube. 2
125, 27, 343, 4096, 512, 64, 729, 8000, 9261, 110592, 226981, 3375, 4410944, 551368, 6644672, 778688, 884736, 9938375, 101194696, 111284641, 12167, 13144256, 14172488, 151419437, 16194277, 17173512, 1815848, 191102976 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

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

FORMULA

a(n) = A030668(A002113(n+1)) = A030679(n)^3. - Robert Israel, Dec 25 2018

MAPLE

N:= 3: # to get extensions of all palindromes of <= N digits

f:= proc(n) local d, x;

  for d from 1 do

    x:= ceil((n*10^d)^(1/3));

    if x^3 < (n+1)*10^d then return x^3 fi

  od

end proc:

digrev:= proc(n) local i, L;

  L:= convert(n, base, 10);

  add(L[-i]*10^(i-1), i=1..nops(L))

end proc:

Res:= seq(f(i), i=1..9):

for d from 2 to N do

if d::even then

    m:= d/2;

    Res:= Res, seq(f(n*10^m + digrev(n)), n=10^(m-1)..10^m-1);

else

    m:= (d-1)/2;

    Res:= Res, seq(seq(f(n*10^(m+1)+y*10^m+digrev(n)), y=0..9), n=10^(m-1)..10^m-1)

fi

od:

Res; # Robert Israel, Dec 25 2018

CROSSREFS

Cf. A002113, A030668, A030679.

Sequence in context: A088403 A077495 A030668 * A028939 A195420 A080538

Adjacent sequences:  A030675 A030676 A030677 * A030679 A030680 A030681

KEYWORD

nonn,base

AUTHOR

Patrick De Geest

STATUS

approved

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Last modified December 5 20:39 EST 2021. Contains 349558 sequences. (Running on oeis4.)