A072395 Numbers n such that reverse(phi(n)) = n.

1, 21, 63, 291, 2991, 6102, 46676013, 69460293, 2346534651, 6313047393, 23400000651, 80050617822, 234065340651, 234659934651, 2340000000651, 2934000006591

Offset: 1

Author

Joseph L. Pe, Jul 21 2002

Keywords

• nonn
• base
• more

Comments

For all n, a(n) = reversal(A085331(n)), so see Comment on A085331. This sequence is a subsequence of A069215 and if m is a term of A069215 and 10 doesn't divide m then m is in this sequence. - Farideh Firoozbakht, Jan 09 2005

a(13) > 10^11. - Donovan Johnson, Feb 03 2012

a(17) > 10^13. - Giovanni Resta, Aug 06 2019

Examples

			reverse(phi(6102)) = reverse(2016) = 6102, so 6102 is a term of the sequence.
		

Crossrefs

Cf. A085331, A069215, A102278.

Programs

Mathematica

Select[Range[10^5], FromDigits[Reverse[IntegerDigits[EulerPhi[#]]]] == # &] (* corrected by Harvey P. Dale, Oct 03 2011 *)

Extensions

More terms from Robert G. Wilson v, Jul 23 2002

More terms from Farideh Firoozbakht, Jan 09 2005

a(10)-a(12) from Donovan Johnson, Feb 03 2012

a(13)-a(16) from Giovanni Resta, Aug 06 2019