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A098770
Abundant numbers whose reversal is a deficient number.
3
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
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
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