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A069215
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Numbers n such that phi(n) = reversal(n).
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12
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1, 21, 63, 270, 291, 2991, 6102, 46676013, 69460293, 2346534651, 6313047393, 23400000651, 80050617822
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| Next term is greater than 210000000. - Farideh Firoozbakht (mymontain(AT)yahoo.com), Aug 31 2004
If 10^n-3 is prime (n is in the sequence A089765) and m=3*(10^n-3) then m is in this sequence, for example 299999999999999991 is a term of this sequence because 299999999999999991=3*(10^17-3) and 17 is in the sequence A089675. So 3*(10^A089675-3) is a subsequence of this sequence, A101700 is this subsequence. - Farideh Firoozbakht (mymontain(AT)yahoo.com), Dec 26 2004
A072395 is a subsequence of this sequence. If m is in the sequence and 10 doesn't divide m then reversal(m) is in the sequence A085331, so see Comments on A085331. - Farideh Firoozbakht (mymontain(AT)yahoo.com), Jan 09 2005
If p=(79*10^(4n+1)-83)/101 is prime then 3p is in the sequence. The proof is easy. 21, 2346534651 & 3*(79*10^2697-83)/101 are the first three such terms. - Farideh Firoozbakht (mymontain(AT)yahoo.com), Apr 22 2008, Aug 16 2008
a(14) > 10^11. - Donovan Johnson, Feb 03 2012
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EXAMPLE
| phi(291) = 192.
phi(6102) = 2016 = reversal(6102), so 6102 belongs to the sequence.
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MATHEMATICA
| Do[If[EulerPhi[n] == FromDigits[Reverse[IntegerDigits[n]]], Print[n]], {n, 1, 10^5}]
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PROG
| (PARI) for( n=1, 1e9, A004086(n)==eulerphi(n) & print1(n", "))
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CROSSREFS
| Cf. A101700, A004086, A000010, A085331, A072395, A101700, A102278.
Sequence in context: A033850 A170930 A113622 * A115921 A072395 A113781
Adjacent sequences: A069212 A069213 A069214 * A069216 A069217 A069218
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KEYWORD
| base,nonn,hard,more,changed
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AUTHOR
| Joseph L. Pe (joseph_l_pe(AT)hotmail.com), Apr 11 2002
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EXTENSIONS
| More terms from Farideh Firoozbakht (mymontain(AT)yahoo.com), Aug 31 2004
One more term from Farideh Firoozbakht (mymontain(AT)yahoo.com), Jan 09 2005
a(11)-a(13) from Donovan Johnson (donovan.johnson(AT)yahoo.com), Feb 03 2012
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