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A062825
Ch(n-th nonprime) where Ch(n) is Chowla's function, cf. A048050.
3
0, 2, 5, 6, 3, 7, 15, 9, 8, 14, 20, 21, 10, 13, 35, 5, 15, 12, 27, 41, 30, 14, 19, 12, 54, 21, 16, 49, 53, 39, 32, 25, 75, 7, 42, 20, 45, 65, 16, 63, 22, 31, 107, 33, 40, 62, 18, 77, 57, 26, 73, 122, 39, 48, 63, 18, 89, 105, 39, 43, 139, 22, 45, 32, 91, 143, 20, 75, 34, 49, 24, 155, 72, 56, 116, 113, 105, 86, 55, 171, 105, 40, 135
OFFSET
1,2
COMMENTS
a(n) = A048050(A018252(n)).
a(n+1) = sum of nontrivial divisors of n-th composite number, or row sums in table A163870. - Juri-Stepan Gerasimov, Aug 06 2009
LINKS
MAPLE
with(numtheory): a_list := proc(n); {$1..n} minus select(isprime, {$1..n}); sort(convert(%, list)); map(f->add(d, d=(divisors(f) minus {1, f})), %) end: a_list(113); # Peter Luschny, Mar 29 2014
MATHEMATICA
Reap[Do[If[!PrimeQ[k], Sow[If[k == 1, 0, DivisorSigma[1, k] - k - 1 ]]], {k, 1, 120}]][[2, 1]] (* Jean-François Alcover, Feb 12 2018 *)
PROG
(PARI) j=[0]; for(n=2, 200, if(isprime(n), n+1, j=concat(j, sigma(n)-n-1))); j
(Haskell)
a062825 1 = 0
a062825 n = sum $ a163870_row (n - 1) -- Reinhard Zumkeller, Mar 29 2014
CROSSREFS
Sequence in context: A336817 A340858 A309364 * A154925 A154962 A091655
KEYWORD
nonn,look,easy
AUTHOR
Jason Earls, Jul 20 2001
EXTENSIONS
Definition revised and a(1) corrected by Reinhard Zumkeller, Mar 29 2014
STATUS
approved