login
A370495
Oblong numbers of the form (k-1)*k where k is the product of an even number of distinct primes.
2
0, 30, 90, 182, 210, 420, 462, 650, 1056, 1122, 1190, 1406, 1482, 2070, 2550, 2970, 3192, 3306, 3782, 4160, 4692, 5402, 5852, 6642, 7140, 7310, 7482, 8190, 8556, 8742, 8930, 11130, 12210, 13110, 13806, 14042, 14762, 15006, 16512, 17556, 17822, 19740, 20022, 20306
OFFSET
1,2
LINKS
FORMULA
a(n) = A002378(A030229(n)-1).
Sum_{n>=2} 1/a(n) = (A368250 - A033150 + 1)/2 = 0.071711363929... .
MATHEMATICA
Table[n*(n - 1), {n, Select[Range[150], MoebiusMu[#] == 1 &]}]
PROG
(PARI) lista(kmax) = forsquarefree(k=1, kmax, if(moebius(k) == 1, print1(k[1]*(k[1]-1), ", ")));
CROSSREFS
Complement of A370494 within A368249.
Sequence in context: A081807 A008445 A039462 * A138018 A004995 A042772
KEYWORD
nonn,easy
AUTHOR
Amiram Eldar, Feb 20 2024
STATUS
approved