

A116030


sigma(n)  phi(n) is a palindrome greater than 2.


2



4, 8, 9, 18, 25, 27, 28, 57, 62, 72, 85, 123, 128, 176, 184, 189, 192, 218, 220, 234, 243, 246, 252, 256, 258, 259, 261, 278, 282, 306, 309, 316, 322, 332, 338, 339, 356, 375, 380, 388, 399, 403, 490, 495, 505, 512, 518, 544, 590, 597, 622, 632, 655, 662
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OFFSET

1,1


COMMENTS

When n is prime sigma(n)phi(n) is 2, so that case is trivial.


LINKS



EXAMPLE

sigma(399)  phi(399) = 424.


MATHEMATICA

pg2Q[n_]:=With[{c=DivisorSigma[1, n]EulerPhi[n]}, PalindromeQ[c]&&c>2]; Select[ Range[700], pg2Q] (* Harvey P. Dale, Jan 16 2023 *)


PROG

(Magma) [n: n in [1..1000]  Intseq(d) eq Reverse(Intseq(d)) and d gt 2 where d is DivisorSigma(1, n)EulerPhi(n)]; // Bruno Berselli, Sep 09 2015


CROSSREFS



KEYWORD

nonn,base


AUTHOR



STATUS

approved



