A117308 - OEIS

A117308

Numbers k for which (phi(k))^2 + phi(k) + 1 is a palindrome.

1, 2, 3, 4, 6, 11, 19, 22, 27, 38, 54, 101, 125, 202, 250, 1111, 1189, 1207, 1243, 1255, 1375, 1405, 1595, 1779, 1875, 1877, 1957, 2008, 2149, 2175, 2222, 2235, 2248, 2272, 2372, 2378, 2384, 2414, 2486, 2500, 2510, 2552, 2750, 2757, 2763, 2781, 2810, 2840

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OFFSET

1,2

LINKS

Table of n, a(n) for n=1..48.

EXAMPLE

19 is in the sequence because (phi(19))^2 + phi(19) + 1 = 18^2 + 18 + 1 = 343, which is a palindrome.

MAPLE

rev:=proc(n) local nn: nn:=convert(n, base, 10): add(nn[nops(nn)+1-j]*10^(j-1), j=1..nops(nn)) end: with(numtheory): a:=proc(m) if rev(phi(m)^2+phi(m)+1)=phi(m)^2+phi(m)+1 then m else fi end: seq(a(m), m=1..3500); # Emeric Deutsch, Apr 30 2006

MATHEMATICA

Select[Range[3000], PalindromeQ[EulerPhi[#]^2+EulerPhi[#]+1]&] (* Harvey P. Dale, Jan 16 2024 *)

CROSSREFS

Sequence in context: A166081 A111124 A295681 * A114412 A352819 A016038

Adjacent sequences: A117305 A117306 A117307 * A117309 A117310 A117311

KEYWORD

base,nonn

AUTHOR

Luc Stevens (lms022(AT)yahoo.com), Apr 24 2006

EXTENSIONS

More terms from Emeric Deutsch, Apr 30 2006

STATUS

approved