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

1,2

Links

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

Example

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

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 *)

Prog

(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

Crossrefs

Cf. A115895, A115896.

Sequence in context: A295393 A120023 A353243 * A116019 A352148 A259561

Adjacent sequences: A115894 A115895 A115896 * A115898 A115899 A115900

Keyword

nonn,base

Author

Giovanni Resta, Feb 06 2006

Status

approved