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Numbers n such that bitor(2*k, sigma(k)) == 2k, where k = A156552(n).
2

%I #6 Mar 15 2019 21:56:28

%S 4,8,9,16,27,30,32,45,64,72,125,128,135,144,243,250,256,270,315,405,

%T 420,480,490,512,576,600,675,756,810,825,875,988,1000,1024,1152,1155,

%U 1210,1215,1458,1470,1600,1690,1716,1728,1920,2048,2100,2187,2250,2430,2450,2475,3125,3234,3240,3600,3645,3825,4320,4375,5070,5103

%N Numbers n such that bitor(2*k, sigma(k)) == 2k, where k = A156552(n).

%H <a href="/index/Bi#binary">Index entries for sequences related to binary expansion of n</a>

%H <a href="/index/Pri#prime_indices">Index entries for sequences computed from indices in prime factorization</a>

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

%o (PARI)

%o A156552(n) = {my(f = factor(n), p2 = 1, res = 0); for(i = 1, #f~, p = 1 << (primepi(f[i, 1]) - 1); res += (p * p2 * (2^(f[i, 2]) - 1)); p2 <<= f[i, 2]); res}; \\ From A156552 by _David A. Corneth_

%o isA324726(n) = ((2*n)==bitor(2*n, sigma(n)));

%o isA324723(n) = if(n>1,isA324726(A156552(n)));

%o (PARI) isA324723(n) = if(1==n,0,my(t=2*A156552(n)); (t==bitor(t,A323243(n)))); \\ Using also code from A323243.

%Y Cf. A156552, A323243, A324722, A324726.

%K nonn

%O 1,1

%A _Antti Karttunen_, Mar 15 2019