A347284 a(n) = Product_{j=1..A089576(n)} p_j^e_j with e_j = floor(e_(j-1)*log(p_(j-1))/log(p_j)) where the first factor is 2^n.
1, 2, 12, 24, 720, 151200, 302400, 1814400, 4191264000, 8382528000, 251727315840000, 503454631680000, 3020727790080000, 1542111744113740800000, 3084223488227481600000, 92526704646824448000000, 555160227880946688000000, 1110320455761893376000000, 10769764221549079560253440000000
Offset: 0
Keywords
Examples
a(0) = 2^0 = 1;
a(1) = 2^1 = 2, since 3^1 > 2^1;
a(2) = 2^2 * 3^1, since 3^1 < 2^2 but 3^2 > 2^2, and since 5^1 > 3^1;
a(3) = 2^3 * 3^1, since 3^1 < 2^3 but 3^2 > 2^3, and 5^1 > 3^1;
a(4) = 2^4 * 3^2 * 5^1, since 3^2 < 2^4 yet 3^3 > 2^4, 5^1 < 3^2 yet 5^2 > 3^2, and 7^1 > 5^1; etc.
Prime shapes of a(n) for 2 <= n <= 5:
5 o
4 o 4 x
3 o 3 x 3 x x
2 x 2 x 2 x x 2 x x x
a(2) 1 X X a(3) 1 X X a(4) 1 X X X a(5) 1 X X X X
2 3 2 3 2 3 5 2 3 5 7
This demonstrates that a(n) is in A025487, that A002110(A001221(a(n))) is the greatest primorial divisor of a(n) as a consequence (prime divisors represented by capital X's), and Chernoff A006939(A001221(a(n))) | n, prime divisors represented by x's of any case. a(n) = A006939(A001221(a(n))) * k, k in A025487, represented by o's.
Because each multiplicity e is necessarily distinct, we may compactify a(n) using Sum_{k=1..omega(a(n))} 2^(e-1).
Prime shapes of a(12):
12 o
11 o
10 o
9 o
8 o
7 o o
6 x o
5 x x
4 x x x
3 x x x x
2 x x x x x
a(12) 1 X X X X X X
2 3 5 7 ...
a(12) = A006939(6) * 2^6 * 3^2
= 5244319080000 * 64 * 9
= 3020727790080000.
O
O x
O x x
O x x o x x
O x x o x x o x x x
O x o x x x x o x x x o x x x x
a(1)*6 = a(2)*2 = a(3)*30 = a(4)*210 = a(5)*2 = a(6), etc., hence a(n) can be generated by a list of indices of primorials {1, 2, 1, 3, 4, 1, 1, 5, ...} and thereby be efficiently compactified.
Links
- Michael De Vlieger, Table of n, a(n) for n = 0..144
- Michael De Vlieger, Bitmap resulting from binary compactification of a(n), 0 <= n <= 4096.
- Michael De Vlieger, Animation of prime shapes of a(n) for 2 <= n <= 37, illustrating a(n) as a product of a particular sequence of primorials.
Crossrefs
Programs
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Mathematica
Array[Times @@ NestWhile[Append[#1, #2^Floor@ Log[#2, #1[[-1]]]] & @@ {#, Prime[Length@ # + 1]} &, {2^#}, Last[#] > 1 &] &, 18, 0] (* or *) Block[{nn = 2^5, a = {}, b, e, i, m, p}, Array[Set[e[#], 0] &, Floor[2^# If[# <= 4, 1/2, -1 + 2^(7/(3 #))]] &[Ceiling@ Log2@ nn]]; Do[e[1]++; b = {2^e[1]}; Do[If[Last[b] == 1, Break[], i = e[j]; p = Prime[j]; While[p^i < b[[j - 1]], i++]; AppendTo[b, p^(i - 1)]; If[i > e[j], e[j]++]], {j, 2, k}]; AppendTo[a, Times @@ b], {k, nn}]; Prepend[a, 1]] (* Generate up to 4096 terms from the bitmap image *) With[{r = ImageData@ Import["https://oeis.org/A347284/a347284.png"]}, {1}~Join~Table[Times @@ Flatten@ MapIndexed[Prime[#2]^#1 &, Reverse@ Position[r[[i]], 0.][[All, 1]]], {i, 20}]] (* Generate up to 10000 terms using b-file at A347354 (numbers are large as n increases, limit nn is set to 120): *) Block[{nn = 120, s, m}, s = Import["https://oeis.org/A347354/b347354.txt", "Data"][[1 ;; nn, -1]]; m = Prime@ Range@ Max[s]; {1}~Join~FoldList[Times, Map[Times @@ m[[1 ;; #]] &, s]]] (* Michael De Vlieger, Sep 25 2021 *)
Formula
Extensions
Definition edited by Peter Munn, May 19 2023
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