A230005 Numbers n such that phi(n) + sigma(n) = reversal(n) - 4.

489, 4629, 296206, 460029, 29589106, 46000029, 2927272726, 4045046518, 21223345084, 29600331295, 296151515206, 460000000029

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

Table of n, a(n) for n=1..12.

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