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A217790 Composite evil numbers (A001969) having no proper evil divisors. 2

%I #32 Nov 13 2019 10:13:17

%S 77,169,209,287,329,343,407,413,427,469,533,553,649,679,703,763,869,

%T 893,917,931,1121,1133,1169,1253,1271,1331,1337,1351,1369,1391,1393,

%U 1457,1477,1501,1517,1589,1631,1661,1757,1781,1813,1829,1963,1991,2033,2191,2209

%N Composite evil numbers (A001969) having no proper evil divisors.

%C The sequence is obtained using Eratosthenes-like sieve for evil numbers.

%C a(10^2) = 4367, a(10^3) = 40247, a(10^4) = 407659, a(10^5) = 4434067. - _Giovanni Resta_, Mar 28 2013

%H Amiram Eldar, <a href="/A217790/b217790.txt">Table of n, a(n) for n = 1..10000</a>

%t evilQ[n_] := EvenQ@Total@IntegerDigits[n, 2]; okQ[n_] := evilQ[n] && ! PrimeQ[n] && Catch[Do[If[evilQ[d], Throw[False]], {d, Most@Rest@Divisors@n}]; True]; Select[Range@3000, okQ] (* _Giovanni Resta_, Mar 28 2013 *)

%o (PARI) isevil(n) = hammingweight(n) % 2 == 0;

%o noevildiv(n) = {fordiv(n, d, if ((d < n) && isevil(d), return (0));); 1;}

%o lista(nn) = {forcomposite(n=1, nn, if (isevil(n) && noevildiv(n), print1(n, ", ")););} \\ _Michel Marcus_, Feb 08 2016

%Y Cf. A000069, A001969.

%K nonn,base

%O 1,1

%A _Vladimir Shevelev_, Mar 28 2013

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Last modified March 28 15:38 EDT 2024. Contains 371254 sequences. (Running on oeis4.)