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Odd numbers k that are multiples of 3 and for which sigma(k) is congruent to 2 modulo 4.
2

%I #10 Feb 13 2022 13:38:59

%S 45,117,153,261,333,369,405,477,549,657,801,873,909,981,1017,1053,

%T 1233,1341,1377,1413,1557,1629,1737,1773,2061,2097,2169,2205,2313,

%U 2349,2421,2493,2529,2637,2817,2853,2925,2997,3033,3141,3177,3321,3357,3501,3573,3609,3645,3681,3789,3825,3897,4041,4113,4149,4293

%N Odd numbers k that are multiples of 3 and for which sigma(k) is congruent to 2 modulo 4.

%H <a href="/index/Si#SIGMAN">Index entries for sequences related to sigma(n)</a>

%t Select[3*Range[1, 1400, 2], Mod[DivisorSigma[1, #], 4] == 2 &] (* _Amiram Eldar_, Feb 13 2022 *)

%o (PARI) isA351533(n) = ((n%2) && !(n%3) && (2 == (sigma(n)%4)));

%Y Intersection of A008585 and A191218. Complement of A351535 in A191218.

%Y Cf. A351534 (subsequence).

%K nonn

%O 1,1

%A _Antti Karttunen_, Feb 13 2022