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A087991 Number of non-palindromic divisors of n. 6
0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 0, 1, 2, 1, 2, 1, 2, 1, 3, 1, 2, 0, 2, 1, 3, 1, 2, 2, 3, 1, 3, 1, 0, 2, 2, 1, 4, 1, 3, 2, 3, 1, 3, 0, 3, 2, 2, 1, 6, 1, 2, 2, 3, 2, 0, 1, 3, 2, 4, 1, 5, 1, 2, 3, 3, 0, 4, 1, 5, 2, 2, 1, 6, 2, 2, 2, 0, 1, 6, 2, 3, 2, 2, 2, 6, 1, 3, 0, 5, 0, 4, 1, 4, 4 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,20

LINKS

Indranil Ghosh, Table of n, a(n) for n = 1..10000

FORMULA

a(n)=A000005[n]-A087990[n].

EXAMPLE

n=132: divisors={1,2,3,4,6,11,12,22,33,44,66,132},

revdivisors={1,2,3,4,6,11,21,22,33,44,66,231}, a[132]=2;

so two of 12 divisors of n are non-palindromic:{21,132}.

MATHEMATICA

palQ[n_] := Reverse[x = IntegerDigits[n]] == x; Table[Count[Divisors[n], _?(! palQ[#] &)], {n, 105}] (* Jayanta Basu, Aug 10 2013 *)

PROG

(Python)

def ispal(n):

....if n==int(str(n)[::-1]):return True

....return False

def A087991(n):

....s=0

....for i in range(1, n+1):

........if n%i==0 and ispal(i)==False:

............s+=1

....return s # Indranil Ghosh, Feb 10 2017

CROSSREFS

Cf. A087990, A062687.

Sequence in context: A284620 A038698 A263233 * A293439 A144095 A076092

Adjacent sequences:  A087988 A087989 A087990 * A087992 A087993 A087994

KEYWORD

nonn,base

AUTHOR

Labos Elemer, Oct 08 2003

STATUS

approved

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Last modified May 26 21:38 EDT 2018. Contains 304645 sequences. (Running on oeis4.)