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Odd numbers k for which A156552(k) < k.
6

%I #18 Aug 11 2023 09:59:14

%S 1,3,5,9,15,21,25,27,35,45,49,55,63,75,77,81,91,99,105,121,125,135,

%T 143,147,165,169,175,187,189,195,221,225,231,243,245,273,275,289,297,

%U 315,323,325,343,351,357,363,375,385,405,425,429,441,455,495,507,525,539,561,567,585,595,605,625,627,637,663,665

%N Odd numbers k for which A156552(k) < k.

%C Odd numbers k such that A005941(k) <= k.

%H Antti Karttunen, <a href="/A364561/b364561.txt">Table of n, a(n) for n = 1..13739; terms less than 2^21</a>

%o (PARI)

%o A156552(n) = { my(f = factor(n), p, 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 };

%o isA364561(n) = ((n%2)&&(A156552(n) < n));

%Y Odd terms in A364560.

%Y Cf. A005940, A005941, A156552, A364545, A364564 (largest prime factor).

%Y Cf. also A364551, A364576 (subsequences).

%K nonn

%O 1,2

%A _Antti Karttunen_, Jul 28 2023