cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

A327685 Nonprime numbers whose prime indices have a common divisor > 1.

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%I A327685 #5 Sep 23 2019 13:43:40
%S A327685 9,21,25,27,39,49,57,63,65,81,87,91,111,115,117,121,125,129,133,147,
%T A327685 159,169,171,183,185,189,203,213,235,237,243,247,259,261,267,273,289,
%U A327685 299,301,303,305,319,321,325,333,339,343,351,361,365,371,377,387,393,399
%N A327685 Nonprime numbers whose prime indices have a common divisor > 1.
%C A327685 First differs from A322336 in lacking 2535 = prime(2)*prime(3)*prime(6)^2.
%C A327685 A prime index of n is a number m such that prime(m) divides n. The multiset of prime indices of n is row n of A112798. Heinz numbers of integer partitions with a common divisor > 1 are A318978, and the enumeration of these partitions by sum is A108572.
%F A327685 Complement of A000040 in A318978.
%e A327685 The sequence of terms together with their prime indices begins:
%e A327685     9: {2,2}
%e A327685    21: {2,4}
%e A327685    25: {3,3}
%e A327685    27: {2,2,2}
%e A327685    39: {2,6}
%e A327685    49: {4,4}
%e A327685    57: {2,8}
%e A327685    63: {2,2,4}
%e A327685    65: {3,6}
%e A327685    81: {2,2,2,2}
%e A327685    87: {2,10}
%e A327685    91: {4,6}
%e A327685   111: {2,12}
%e A327685   115: {3,9}
%e A327685   117: {2,2,6}
%e A327685   121: {5,5}
%e A327685   125: {3,3,3}
%e A327685   129: {2,14}
%e A327685   133: {4,8}
%e A327685   147: {2,4,4}
%t A327685 Select[Range[100],#>1&&!PrimeQ[#]&&GCD@@PrimePi/@First/@FactorInteger[#]>1&]
%Y A327685 Cf. A000837, A007916, A018783, A056239, A108572, A112798, A289509, A318978, A327407, A327658.
%K A327685 nonn
%O A327685 1,1
%A A327685 _Gus Wiseman_, Sep 22 2019