A351534 - OEIS

%I #8 Feb 13 2022 13:38:44

%S 45,261,369,909,1017,1233,1341,1557,2313,2529,2637,2853,3177,3501,

%T 3609,4149,4293,4581,5121,5445,5553,5733,5769,5877,6093,6525,6849,

%U 7173,7389,7713,8361,8469,8793,9117,9225,9441,9981,10629,10737,10953,11061,11601,11709,12249,12357,12681,12897,13005,13329,13977,14517

%N Odd numbers for which sigma(k) is congruent to 2 modulo 4 and the 3-adic valuation of k is one larger than the 3-adic valuation of sigma(k).

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

%t Select[Range[1, 15000, 2], Mod[(s = DivisorSigma[1, #]), 4] == 2 && IntegerExponent[#, 3] - IntegerExponent[s, 3] == 1 &] (* _Amiram Eldar_, Feb 13 2022 *)

%o (PARI) isA351534(n) = if(!(n%2),0,my(s=sigma(n)); (2 == (s%4)) && (valuation(n,3) == (1+valuation(s,3))));

%Y Subsequence of A351533, which is intersection of A008585 and A191218.

%Y Cf. A000203, A007949, A351536.

%K nonn

%O 1,1

%A _Antti Karttunen_, Feb 13 2022