A116030 sigma(n) - phi(n) is a palindrome greater than 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

Offset: 1

Author

Giovanni Resta, Feb 13 2006

Keywords

• nonn
• base

Comments

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

Examples

			sigma(399) - phi(399) = 424.
		

Links

• Harvey P. Dale, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A115897, A116031.

Programs

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

Mathematica

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