The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation. Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A329661 BII-number of the set-system whose MM-number is A329629(n). 3
 0, 1, 2, 8, 4, 3, 128, 16, 32768, 9, 5, 2147483648, 256, 32, 129, 10, 9223372036854775808, 6, 170141183460469231731687303715884105728, 512, 65536, 57896044618658097711785492504343953926634992332820282019728792003956564819968, 130, 17, 32769, 4294967296 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS A binary index of n is any position of a 1 in its reversed binary expansion. The binary indices of n are row n of A048793. We define the set-system with BII-number n to be obtained by taking the binary indices of each binary index of n. Every set-system (finite set of finite nonempty sets of positive integers) has a different BII-number. For example, 18 has reversed binary expansion (0,1,0,0,1), and since the binary indices of 2 and 5 are {2} and {1,3} respectively, the BII-number of {{2},{1,3}} is 18. Elements of a set-system are sometimes called edges. 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. The multiset of multisets with MM-number n is formed by taking the multiset of prime indices of each part of the multiset of prime indices of n. For example, the prime indices of 78 are {1,2,6}, so the multiset of multisets with MM-number 78 is {{},{1},{1,2}}. LINKS FORMULA A326031(a(n)) = A302242(A329629(n)). EXAMPLE The sequence of all set-systems together with their MM-numbers and BII-numbers begins:              {}:  1 ~ 0           {{1}}:  3 ~ 1           {{2}}:  5 ~ 2           {{3}}: 11 ~ 8         {{1,2}}: 13 ~ 4       {{1},{2}}: 15 ~ 3           {{4}}: 17 ~ 128         {{1,3}}: 29 ~ 16           {{5}}: 31 ~ 32768       {{1},{3}}: 33 ~ 9     {{1},{1,2}}: 39 ~ 5           {{6}}: 41 ~ 2147483648         {{1,4}}: 43 ~ 256         {{2,3}}: 47 ~ 32       {{1},{4}}: 51 ~ 129       {{2},{3}}: 55 ~ 10           {{7}}: 59 ~ 9223372036854775808     {{2},{1,2}}: 65 ~ 6           {{8}}: 67 ~ 170141183460469231731687303715884105728         {{2,4}}: 73 ~ 512 MATHEMATICA fbi[q_]:=If[q=={}, 0, Total[2^q]/2]; primeMS[n_]:=If[n==1, {}, Flatten[Cases[FactorInteger[n], {p_, k_}:>Table[PrimePi[p], {k}]]]]; das=Select[Range, OddQ[#]&&SquareFreeQ[#]&&And@@SquareFreeQ/@primeMS[#]&]; Table[fbi[fbi/@primeMS/@primeMS[n]], {n, das}] CROSSREFS MM-numbers of set-systems are A329629. Cf. A000120, A005117, A048793, A056239, A070939, A112798, A302242, A302494, A326031, A329557. Classes of MM-numbers: A305078 (connected), A316476 (antichains), A318991 (chains), A320456 (covers), A329559 (clutters). Classes of BII-numbers: A326701 (set partitions), A326703 (chains), A326704 (antichains), A326749 (connected), A326752 (hypertrees), A326754 (covers). Sequence in context: A085993 A010595 A109594 * A254446 A197486 A086311 Adjacent sequences:  A329658 A329659 A329660 * A329663 A329664 A329665 KEYWORD nonn AUTHOR Gus Wiseman, Nov 19 2019 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified March 29 15:16 EDT 2020. Contains 333107 sequences. (Running on oeis4.)