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A169730 Write the n-th squarefree semiprime as prime(m)*prime(k). Then a(n) is the absolute value of prime(m)*k-prime(k)*m. 1
1, 1, 1, 1, 2, 1, 1, 7, 3, 1, 3, 8, 5, 13, 8, 14, 9, 9, 9, 19, 13, 9, 15, 16, 15, 28, 10, 29, 17, 17, 21, 38, 24, 25, 19, 25, 43, 44, 20, 29, 49, 31, 1, 37, 31, 38, 35, 58, 29, 37, 67, 41, 68, 51, 8, 47, 77, 49, 46, 58, 49, 7, 82, 51, 59, 47, 51, 83, 11, 53, 66, 92 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,5
LINKS
EXAMPLE
a(1)=1 because prime(1)*2-prime(2)*1=4-3=1; a(2)=1 because prime(1)*3-prime(3)*2=6-5=1.
MAPLE
A006881 := proc(n)
option remember;
if n = 1 then
6;
else
for a from procname(n-1)+1 do
if numtheory[bigomega](a)=2 and issqrfree(a) then
return a;
end if;
end do:
end if;
end proc:
A169730 := proc(n)
local p, k, pm, pk;
p := numtheory[factorset](A006881(n)) ;
pm := op(1, p) ;
pk := op(2, p) ;
k := numtheory[pi](pk) ;
m := numtheory[pi](pm) ;
abs(pm*k-pk*m) ;
end proc:
seq(A169730(n), n=1..72) ; # R. J. Mathar, Jun 02 2016
CROSSREFS
Cf. A006881.
Sequence in context: A301922 A144510 A143670 * A220725 A333142 A196832
KEYWORD
nonn,less
AUTHOR
EXTENSIONS
Corrected by R. J. Mathar, Jun 02 2016
STATUS
approved

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Last modified May 23 02:30 EDT 2024. Contains 372758 sequences. (Running on oeis4.)