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A178323 Numbers n such that phi(reversal(n)) + sigma(reversal(n)) = n. 0
572, 592, 5992, 599992, 2014080, 5999992, 594637872, 599999992, 599999999992 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
If n is in the sequence A070272 then reversal(n) is in this sequence. 10 divides all other terms of the sequence. 2014080 is the only known such term.
If p=6*10^n-1 is a prime greater than 5 then reversal(5*p) is in the sequence, see comment lines of A070272.
There is no further term up to 10^9.
10^12 < a(10) <= 1442827967760. - Giovanni Resta, Sep 04 2018
LINKS
EXAMPLE
2014080 = phi(804102) + sigma(804102), so 2014080 is in the sequence.
MATHEMATICA
r[n_]:=FromDigits[Reverse[IntegerDigits[n]]];
Do[If[EulerPhi[r[n]]+DivisorSigma[1, r[n]]==n, Print[n]], {n, 1000000000}]
CROSSREFS
Sequence in context: A251384 A076465 A144956 * A049361 A252633 A175989
KEYWORD
nonn,base,more
AUTHOR
Farideh Firoozbakht, May 28 2010
EXTENSIONS
a(9) from Giovanni Resta, Sep 04 2018
STATUS
approved

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Last modified March 28 15:28 EDT 2024. Contains 371254 sequences. (Running on oeis4.)