A115897 Numbers k such that sigma(k) + phi(k) is a palindrome.

1, 2, 3, 4, 10, 11, 21, 49, 92, 101, 115, 131, 145, 186, 200, 201, 206, 207, 221, 226, 227, 240, 272, 302, 310, 313, 327, 342, 344, 370, 374, 388, 403, 406, 409, 413, 419, 425, 439, 449, 880, 948, 1015, 1055, 1132, 1165, 1385, 1443, 1680, 1755, 1785

Offset: 1

Author

Giovanni Resta, Feb 06 2006

Keywords

• nonn
• base

Examples

			sigma(1055) + phi(1055) = 1272 + 840 = 2112.
		

Links

• Michael De Vlieger, Table of n, a(n) for n = 1..5000

Crossrefs

Cf. A115895, A115896.

Programs

Mathematica

Select[Range@ 1800, Reverse@ # == # &@ IntegerDigits[DivisorSigma[1, #] + EulerPhi@ #] &] (* Michael De Vlieger, Jul 22 2016 *)
Select[Range[2000],PalindromeQ[DivisorSigma[1,#]+EulerPhi[#]]&] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Mar 29 2020 *)

PARI

ispal(n)=n=digits(n); Vecrev(n)==n
is(n,f=factor(n))=ispal(sigma(f)+eulerphi(f)) \\ Charles R Greathouse IV, Jul 22 2016