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.
%I A340104 #14 Mar 17 2021 08:02:08
%S A340104 1,2,7,13,14,19,23,26,29,37,38,43,46,47,53,58,61,71,73,74,79,86,89,91,
%T A340104 94,97,101,103,106,107,113,122,131,133,137,139,142,146,149,151,158,
%U A340104 161,163,167,173,178,181,182,193,194,197,199,202,203,206,214,223,226
%N A340104 Products of distinct primes of nonprime index (A007821).
%C A340104 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.
%F A340104 Equals A005117 /\ A320628.
%e A340104 The sequence of terms together with the corresponding prime indices of prime indices begins:
%e A340104 1: {} 58: {{},{1,3}} 113: {{1,2,3}}
%e A340104 2: {{}} 61: {{1,2,2}} 122: {{},{1,2,2}}
%e A340104 7: {{1,1}} 71: {{1,1,3}} 131: {{1,1,1,1,1}}
%e A340104 13: {{1,2}} 73: {{2,4}} 133: {{1,1},{1,1,1}}
%e A340104 14: {{},{1,1}} 74: {{},{1,1,2}} 137: {{2,5}}
%e A340104 19: {{1,1,1}} 79: {{1,5}} 139: {{1,7}}
%e A340104 23: {{2,2}} 86: {{},{1,4}} 142: {{},{1,1,3}}
%e A340104 26: {{},{1,2}} 89: {{1,1,1,2}} 146: {{},{2,4}}
%e A340104 29: {{1,3}} 91: {{1,1},{1,2}} 149: {{3,4}}
%e A340104 37: {{1,1,2}} 94: {{},{2,3}} 151: {{1,1,2,2}}
%e A340104 38: {{},{1,1,1}} 97: {{3,3}} 158: {{},{1,5}}
%e A340104 43: {{1,4}} 101: {{1,6}} 161: {{1,1},{2,2}}
%e A340104 46: {{},{2,2}} 103: {{2,2,2}} 163: {{1,8}}
%e A340104 47: {{2,3}} 106: {{},{1,1,1,1}} 167: {{2,6}}
%e A340104 53: {{1,1,1,1}} 107: {{1,1,4}} 173: {{1,1,1,3}}
%t A340104 Select[Range[100],SquareFreeQ[#]&&FreeQ[If[#==1,{},FactorInteger[#]],{p_,k_}/;PrimeQ[PrimePi[p]]]&]
%Y A340104 These primes (of nonprime index) are listed by A007821.
%Y A340104 The non-strict version is A320628, with odd case A320629.
%Y A340104 The odd case is A340105.
%Y A340104 The prime instead of nonprime version:
%Y A340104 primes: A006450
%Y A340104 products: A076610
%Y A340104 strict: A302590
%Y A340104 The semiprime instead of nonprime version:
%Y A340104 primes: A106349
%Y A340104 products: A339112
%Y A340104 strict: A340020
%Y A340104 The squarefree semiprime instead of nonprime version:
%Y A340104 strict: A309356
%Y A340104 primes: A322551
%Y A340104 products: A339113
%Y A340104 A056239 gives the sum of prime indices, which are listed by A112798.
%Y A340104 A257994 counts prime prime indices.
%Y A340104 A302242 is the weight of the multiset of multisets with MM-number n.
%Y A340104 A305079 is the number of connected components for MM-number n.
%Y A340104 A320911 lists products of squarefree semiprimes (Heinz numbers of A338914).
%Y A340104 A320912 lists products of distinct semiprimes (Heinz numbers of A338916).
%Y A340104 A330944 counts nonprime prime indices.
%Y A340104 A330945 lists numbers with a nonprime prime index (nonprime case: A330948).
%Y A340104 A339561 lists products of distinct squarefree semiprimes (A339560).
%Y A340104 MM-numbers: A255397 (normal), A302478 (set multisystems), A320630 (set multipartitions), A302494 (sets of sets), A305078 (connected), A316476 (antichains), A318991 (chains), A320456 (covers), A328514 (connected sets of sets), A329559 (clutters), A340019 (half-loop graphs).
%Y A340104 Cf. A000040, A000720, A001055, A001222, A003963, A005117, A007097, A018252, A289509, A320461, A320631.
%K A340104 nonn
%O A340104 1,2
%A A340104 _Gus Wiseman_, Mar 12 2021