cp's OEIS Frontend

A351538 Numbers k such that both k and sigma(k) are congruent to 2 modulo 4 and the 3-adic valuation of sigma(k) is exactly 1.

%I A351538 #15 Feb 19 2022 10:23:34
%S A351538 26,74,122,146,194,218,234,314,362,386,458,482,554,626,650,666,674,
%T A351538 698,746,794,818,842,866,914,1082,1098,1154,1202,1226,1314,1322,1346,
%U A351538 1418,1466,1514,1538,1658,1706,1746,1754,1850,1874,1962,1994,2018,2042,2066,2106,2138,2186,2234,2258,2306,2402,2426,2474,2498
%N A351538 Numbers k such that both k and sigma(k) are congruent to 2 modulo 4 and the 3-adic valuation of sigma(k) is exactly 1.
%C A351538 All the terms of the form 4u+2 in A349745 (if they exist) are found in this sequence. As A351537 is the intersection of A191218 and A329963, and the latter has asymptotic density zero, so has this sequence also. It is conjectured that A351555(a(n)) is nonzero for all n, which would imply that the intersection with A349745 is empty. - _Antti Karttunen_, Feb 19 2022
%H A351538 Antti Karttunen, <a href="/A351538/b351538.txt">Table of n, a(n) for n = 1..25000</a>
%H A351538 <a href="/index/Si#SIGMAN">Index entries for sequences related to sigma(n)</a>
%F A351538 a(n) = 2 * A351537(n).
%o A351538 (PARI) isA351538(n) = if(!(2==(n%4)),0, my(s=sigma(n)); (2 == (s%4)) && (1==valuation(s,3)));
%Y A351538 Cf. A191218, A329963, A349745, A351537.
%Y A351538 Probably a subsequence of A351543. (See also A351550, A351555).
%K A351538 nonn
%O A351538 1,1
%A A351538 _Antti Karttunen_, Feb 14 2022