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A099280
2^n-th palindromic number.
3
1, 2, 4, 8, 77, 232, 555, 2992, 15751, 41314, 92529, 1049401, 3097903, 7193917, 63855836, 227696722, 555373555, 3107337013, 16214541261, 42428982424, 94857775849, 1097153517901, 3194305034913, 7388609068837, 67772177127776
OFFSET
0,2
MATHEMATICA
NextPalindrome[n_] := Block[ {l = Floor[ Log[10, n] + 1], idn = IntegerDigits[n]}, If[ Union[ idn] == {9}, Return[n + 2], If[l < 2, Return[n + 1], If[ FromDigits[ Reverse[ Take[ idn, Ceiling[l/2]]]] FromDigits[ Take[ idn, -Ceiling[l/2]]], FromDigits[ Join[ Take[ idn, Ceiling[l/2]], Reverse[ Take[ idn, Floor[l/2]]] ]], idfhn = FromDigits[ Take[ idn, Ceiling[l/2]]] + 1; idp = FromDigits[ Join[ IntegerDigits[ idfhn], Drop[ Reverse[ IntegerDigits[ idfhn]], Mod[l, 2]]]] ]]]]; k = 1; np = 0; Do[ While[np = NextPalindrome[np]; k != 2^n, k++ ]; Print[np], {n, 26}]
PROG
(Python)
def A099280(n):
if n == 0: return 1
m = 1<<n-1
k = (m<<1)+1
y = 10*(x:=10**(len(str(m))-1))
return (c:=k-x)*x+int(str(c)[-2::-1]or 0) if k<x+y else (c:=k-y)*y+int(str(c)[-1::-1]or 0) # Chai Wah Wu, Jun 13 2024
CROSSREFS
Cf. A083816.
Sequence in context: A204548 A018532 A270381 * A018560 A087375 A018580
KEYWORD
base,nonn
AUTHOR
Robert G. Wilson v, Oct 04 2004
STATUS
approved