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 A230005 Numbers n such that phi(n) + sigma(n) = reversal(n) - 4. 6
 489, 4629, 296206, 460029, 29589106, 46000029, 2927272726, 4045046518, 21223345084, 29600331295, 296151515206, 460000000029 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS If p = 15*10^k+10+(10^k-1)/3 is prime then 3*p is in the sequence. a(7) is greater than 1.3*10^8. a(11) > 10^11. - Donovan Johnson, Nov 08 2013 If p=(1/11)*(23*100^m-1) is prime then 14*p is a term of the sequence. - Farideh Firoozbakht, Nov 08 2013 a(13) > 10^13. - Giovanni Resta, Feb 08 2014 If p = (1685*10^(2k+2)+31)/33 is prime then 58*p is in the sequence. For k = 0, 3, 9, 30, 42, 51, 120, 846, ... p is prime. - Farideh Firoozbakht, Feb 10 2014 LINKS EXAMPLE 489 is in the sequence because phi(489)+sigma(489) = 324+656 = 984-4 = reversal(489)-4. MATHEMATICA Do[If[FromDigits@Reverse@IntegerDigits@n-4 == EulerPhi[n] + DivisorSigma[1, n], Print[n]], {n, 130000000}] PROG (PARI) is(n)=subst(Polrev(digits(n)), 'x, 10)-4==eulerphi(n)+sigma(n) \\ Charles R Greathouse IV, Nov 08 2013 CROSSREFS Cf. A000010, A000203, A004086, A070272, A230004, A230006, A230019, A136544, A237521, A237522. Sequence in context: A201215 A214807 A251676 * A221940 A221739 A068751 Adjacent sequences:  A230002 A230003 A230004 * A230006 A230007 A230008 KEYWORD nonn,base,more AUTHOR Farideh Firoozbakht, Nov 07 2013 EXTENSIONS a(7)-a(10) from Donovan Johnson, Nov 08 2013 a(11)-a(12) from Giovanni Resta, Feb 06 2014 STATUS approved

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Last modified December 5 00:11 EST 2021. Contains 349527 sequences. (Running on oeis4.)