OFFSET
0,2
COMMENTS
There exist an infinity of 1's, 2's, 6's, 30's, 42's, 66's, ... .
Respective ranks:
0, 3, 7, 11, 15, 19, ...
1, 5, 9, 13, 17, 21, ... (= A016813)
2, 14, 26, 34, 38, 62, ... (= A051222)
4, 8, 68, 76, 124, 152, ... (= A051226)
6, 114, 186, 258, 354, 402, ... (= A051228)
10, 50, 170, 370, 470, 590, ... (= A051230)
12, 24, 1308, 1884, 2004, 2364, ... (= A249134)
etc.
Hence by antidiagonals a permutation of A001477(n).
First column: A248614(n).
a(n) is an alternative sequence for the denominators of the Bernoulli numbers.
First 36 terms of the corresponding clockwise spiral:
.
330------2----138------1---2730------2
| |
| |
1 42------1-----30------2 6
| | | |
| | | |
798 2 1------2 66 1
| | | | |
| | | | |
2 30------1------6 1 870
| | |
| | |
510------1------6------2---2730 2
|
|
1------6------2----510------1--14322
MAPLE
Clausen := proc(n) local S, i;
S := numtheory[divisors](n); S := map(i->i+1, S);
S := select(isprime, S); mul(i, i=S) end:
A249306 := n -> `if`(n mod 4 = 3, 1, Clausen(n)):
seq(A249306(n), n=0..59); # Peter Luschny, Nov 10 2014
MATHEMATICA
a[n_] := Denominator[BernoulliB[n]]; a[n_ /; Mod[n, 4] == 1] = 2; Table[a[n], {n, 0, 60}] (* Jean-François Alcover, Oct 28 2014 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul Curtz, Oct 28 2014
STATUS
approved