0,2

This is to quadruple factorial A007662 = n!!!!, as double primorial A079078 = n## is to double factorial A006882 = n!!, and as primorial A002110 = n# is to factorial A000142 = n!. There is an obvious generalization to multiprimorial. (n####)*((n-1)####)*((n-2)####)*((n-3)####) = n#. n#### is a k-almost prime for k = ceiling(n/4).

Eric Weisstein's World of Mathematics, Primorial.

Eric Weisstein's World of Mathematics, Multifactorial.

a(n) = n#### = prime(n)*((n-4)####) = Prod[i == n mod 4, to n] prime(i). Notationally, prime(0) = 1; (-n)#### = 0#### = 1.

n#### is also written n#4.

0#### = p(0) = 1.

1#### = p(1) = 2.

2#### = p(2) = 3.

3#### = p(3) = 5.

4#### = p(4)p(0) = 7*1 = 7.

5#### = p(5)p(1) = 11*2 = 22.

6#### = p(6)p(2) = 13*3 = 39.

7#### = p(7)p(3) = 17*5 = 85.

8#### = p(8)p(4)p(0) = 19*7*1 = 133.

9#### = p(9)p(5)p(1) = 23*11*2 = 506.

10#### = p(10)p(6)p(2) = 29*13*3 = 1131.

11#### = p(11)p(7)p(3) = 31*17*5 = 2635.

12#### = 37*19*7*1 = 4921.

13#### = 41*23*11*2 = 20746.

14#### = 43*29*13*3 = 48633.

15#### = 47*31*17*5 = 123845.

16#### = 53*37*19*7*1 = 260813.

17#### = 59*41*23*11*2 = 1224014.

18#### = 61*43*29*13*3 = 2966613.

19#### = 67*47*31*17*5 = 8297615.

20#### = 71*53*37*19*7*1 = 18517723.

21#### = 73*59*41*23*11*2 = 89353022.

22#### = 79*61*43*29*13*3 = 234362427.

23#### = 83*67*47*31*17*5 = 688702045.

24#### = 89*71*53*37*19*7*1 = 1648077347.

25#### = 97*73*59*41*23*11*2 = 8667243134.

26#### = 101*79*61*43*29*13*3 = 23670605127.

27#### = 103*83*67*47*31*17*5 = 70936310635.

28#### = 107*89*71*53*37*19*7*1 = 176344276129.

Cf. A000142, A002110, A006882, A007661, A007662, A079078.

Adjacent sequences: A114417 A114418 A114419 this_sequence A114421 A114422 A114423

Sequence in context: A084983 A062239 A066483 this_sequence A113590 A124673 A024776

easy,nonn

Jonathan Vos Post (jvospost2(AT)yahoo.com), Feb 12 2006