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 A104906 Numbers n such that d(n)*reversal(n)=phi(n), where d(n) is number of positive divisors of n. 2
 1, 10, 831, 8310 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS If n is a term of this sequence and gcd(10,n)=1 then 10*n is also in the sequence because reversal(10*n)=reversal(n); d(10)=phi(10) and both functions d & phi are multiplicative. No further terms up to 350000000. a(5) > 10^12. - Giovanni Resta, Apr 25 2017 LINKS Table of n, a(n) for n=1..4. EXAMPLE 8310 is in the sequence because d(8310)=16; reversal(8310)=138; phi(8310)=2208 & 16*138=2108. MATHEMATICA reversal[n_]:= FromDigits[Reverse[IntegerDigits[n]]]; Do[If[DivisorSigma[0, n]*reversal[n] == EulerPhi[n], Print[n]], {n, 350000000}] CROSSREFS Cf. A063903, A104904, A104905, A104907. Sequence in context: A054944 A272854 A015093 * A013386 A013385 A013383 Adjacent sequences: A104903 A104904 A104905 * A104907 A104908 A104909 KEYWORD more,nonn AUTHOR Farideh Firoozbakht, Apr 14 2005 STATUS approved

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Last modified June 9 23:14 EDT 2023. Contains 363183 sequences. (Running on oeis4.)