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

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

Offset

1,2

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

Links

Table of n, a(n) for n=1..16.

Example

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

Mathematica

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

Prog

(PARI) isok(k) = fromdigits(Vecrev(digits(eulerphi(k)))) == k; \\ Michel Marcus, Oct 31 2025

Crossrefs

Cf. A000010, A004086, A085331, A069215, A102278.

Sequence in context: A069215 A115921 A251808 * A113781 A299450 A300088

Adjacent sequences: A072392 A072393 A072394 * A072396 A072397 A072398

Keyword

nonn,base,more

Author

Joseph L. Pe, Jul 21 2002

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

Status

approved