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 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS When n is prime sigma(n)-phi(n) is 2, so that case is trivial. LINKS Harvey P. Dale, Table of n, a(n) for n = 1..1000 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 Cf. A115897, A116031. Sequence in context: A257009 A071592 A089765 * A116020 A354869 A213015 Adjacent sequences: A116027 A116028 A116029 * A116031 A116032 A116033 KEYWORD nonn,base AUTHOR Giovanni Resta, Feb 13 2006 STATUS approved

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Last modified December 10 18:12 EST 2023. Contains 367717 sequences. (Running on oeis4.)