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

1,1

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