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A178540 a(n) is the smallest n-digit non-palindromic number m such that sum of the prime factors of m is equal to sum of the prime factors of reversal(m). 0
45, 250, 1131, 12441, 109416, 1002921, 10009577, 100022593, 1000081008, 10000401424, 100000835544, 1000001449713, 10000013519782, 100000013605380, 1000000081310530 (list; graph; refs; listen; history; text; internal format)
OFFSET

2,1

COMMENTS

If 10 doen't divide n, number of digits of n is l and both numbers n & reversal(n) have the same sum of prime factors then for all positive numbers k, n*(10^(k*l)-1)/(10^l-1) has the same property (See the mentioned link).

LINKS

Table of n, a(n) for n=2..16.

Carlos Rivera SOPF(N)=SOP(RN)

EXAMPLE

250 = 2*5*5*5, reversal(250) = 2*2*13, sum of the prime factors of both these are equal, namely 17 and since 250 is the smallest 3-digit number with this property, so

a(3) = 250.

MATHEMATICA

r[n_]:=FromDigits[Reverse[IntegerDigits[n]]]; sop[n_]:=(b=FactorInteger[n]; l=Length[b]; Sum[b[[k]][[1]]*b[[k]][[2]], {k, l}]); a[n_]:=(For[k=1, 10^(n-1)+kŠr[10^(n-1)+k]||sop[10^(n-1)+k]¹sop[r[10^(n-1)+k]], k++]; 10^(n-1)+k)

CROSSREFS

Cf. A001414, A004086.

Sequence in context: A172118 A127073 A089549 * A351534 A296326 A064561

Adjacent sequences: A178537 A178538 A178539 * A178541 A178542 A178543

KEYWORD

nonn,base

AUTHOR

J. M. Bergot & Farideh Firoozbakht, Dec 24 2010

STATUS

approved

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Last modified December 5 02:30 EST 2022. Contains 358572 sequences. (Running on oeis4.)