cp's OEIS Frontend

A133688 Least odd primitive abundant number with 3^n as a divisor, but not 3^(n+1).

%I A133688 #26 Nov 28 2024 14:42:16
%S A133688 5391411025,5775,1575,945,81081,78975,1468935,6375105,436444281,
%T A133688 5356826865,21873816315,371922783705,2241870572475,158639164165575,
%U A133688 297836412308955,1429674513582825,13431279259253115,100139192108634825
%N A133688 Least odd primitive abundant number with 3^n as a divisor, but not 3^(n+1).
%e A133688 5391411025=3^0 * 5^2 * 7 * 11 * 13 * 17 * 19 * 23 * 29 least odd abundant number with no factor 3.
%e A133688 5775 = 3^1 * 5^2 * 7 * 11.
%e A133688 1575 = 3^2 * 5^2 * 13.
%e A133688 945 = 3^3 * 5 * 7.
%e A133688 81081 = 3^4 * 7 * 11 * 13.
%e A133688 78975 = 3^5 * 5^2 * 13.
%e A133688 1468935 = 3^6 * 5 * 13 * 31.
%e A133688 6375105 = 3^7 * 5 * 11 * 53.
%e A133688 436444281 = 3^8 * 7 * 13 * 17 * 43.
%o A133688 (PARI)
%o A133688 isprab(v) = {my(sig = sigma(v)); if (sig < 2*v, return (0)); if (sig == 2*v, return (1)); fordiv (v, d, if ((d != v) && (sigma(d)>=2*d), return (0));); return (1);}
%o A133688 a(n) = {my(p = 3^n, k = 1); while (1, if (k % 3 != 0, v = p * k; if (isprab(v), return (v));); k += 2;);}
%o A133688 \\ _Michel Marcus_, Mar 07 2013
%Y A133688 Cf. A006038 (odd primitive abundant numbers).
%Y A133688 Cf. A115414 (odd abundant numbers not divisible by 3).
%K A133688 nonn,more
%O A133688 0,1
%A A133688 _Pierre CAMI_, Jan 04 2008
%E A133688 Some terms corrected and a(9)-a(13) from _Michel Marcus_, Mar 07 2013
%E A133688 a(14)-a(17) from _David A. Corneth_, Oct 26 2024