cp's OEIS Frontend

A291422 List of pairs of amicable numbers (m,n) where the sum of the pair is divisible by 10.

%I A291422 #72 Feb 16 2025 08:33:50
%S A291422 6232,6368,10744,10856,12285,14595,66928,66992,67095,71145,79750,
%T A291422 88730,100485,124155,122265,139815,122368,123152,141664,153176,142310,
%U A291422 168730,176272,180848,185368,203432,356408,399592,437456,455344,522405,525915,600392,669688,609928,686072
%N A291422 List of pairs of amicable numbers (m,n) where the sum of the pair is divisible by 10.
%C A291422 The sequence lists those amicable pairs (m,n) in increasing order where the sum of the amicable pair is divisible by ten.
%C A291422 Up to the first 5001 amicable pairs, 88.1% of the sums satisfy this condition (up to the first 100 amicable pairs: 74%; up to the first 1000: 82.5%; up to 2000: 85.25%).  So the conjecture here is that as the number of the amicable numbers approaches infinity, the percentage of the sums of the amicable pairs divisible by ten approaches 100%. [corrected by _Paul Zimmermann_, Feb 05-06 2019]
%C A291422 Among the 1947667 pairs up to 19 digits from Sergei Chernykh's database, there are 1872573 pairs with m+n divisible by ten, thus about 96.14%. - _Paul Zimmermann_, Feb 07 2019
%D A291422 Richard K. Guy, Unsolved Problems in Number Theory, Springer-Verlag, 1994, pp. 55-58.
%D A291422 Eric W. Weisstein, CRC Concise Encyclopedia of Mathematics, Chappman and HALL/CRC, 2003, pp. 67-69.
%H A291422 Amiram Eldar, <a href="/A291422/b291422.txt">Table of n, a(n) for n = 1..10000</a>
%H A291422 Sergei Chernykh, <a href="http://sech.me/ap/">Amicable pairs list</a>.
%H A291422 Zoltan Galantai, <a href="/A291422/a291422_2.txt">List of the amicable pairs where the sum divisible by ten</a> smaller and larger amicable numbers; sums (the first 4406 pairs).
%H A291422 Zoltan Galantai, <a href="/A291422/a291422_3.txt">List of the first 5001 amicable pairs with their sums</a> denoting whether the sum is divisible by ten or not.
%H A291422 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/AmicablePair.html">Amicable Pair</a>.
%H A291422 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/SociableNumbers.html">Sociable Numbers</a>.
%e A291422 The sum of 6232 and 6368 is divisible by ten, thus the (6232, 6368) amicable pair belongs to the sequence. On the other hand, the (220, 284) amicable pair does not qualify since its sum is 504.
%o A291422 (PARI) lista(nn) = {for (n=1, nn, spd = sigma(n)-n; if ((spd > n) && (sigma(spd)-spd == n) && !((n + spd) % 10), print1(n, ", ", spd, ", ")););} \\ _Michel Marcus_, Aug 26 2017
%Y A291422 Cf. A002025, A002046, A063990, A180164, A259180, A259933, A291550.
%K A291422 nonn,tabf
%O A291422 1,1
%A A291422 _Zoltan Galantai_, Aug 22 2017