A098770 Abundant numbers whose reversal is a deficient number.

12, 18, 20, 30, 36, 40, 54, 56, 70, 72, 78, 80, 90, 96, 100, 102, 104, 108, 112, 114, 120, 126, 132, 138, 140, 144, 150, 156, 160, 162, 168, 174, 176, 180, 186, 192, 196, 198, 200, 208, 220, 224, 260, 280, 300, 304, 306, 308, 312, 318, 320, 324, 330, 336, 340

Offset

1,1

Links

Amiram Eldar, Table of n, a(n) for n = 1..10000

Example

a(2) = 18 because 18 is the second abundant number which on reversing its digits gives a deficient number, namely 81.

Mathematica

rev[n_] := FromDigits @ Reverse @ IntegerDigits[n]; Select[Range[340], DivisorSigma[1, #] > 2*# && DivisorSigma[1, (r = rev[#])] < 2*r &] (* Amiram Eldar, Aug 26 2020 *)

Crossrefs

Cf. A004086, A005100, A005101, A098768.

Sequence in context: A340780 A054753 A098899 * A333928 A357695 A192819

Adjacent sequences: A098767 A098768 A098769 * A098771 A098772 A098773

Keyword

easy,nonn,base

Author

Shyam Sunder Gupta, Oct 02 2004

Extensions

Edited by N. J. A. Sloane at the suggestion of Andrew S. Plewe, May 21 2007

Status

approved