A062825 Ch(n-th nonprime) where Ch(n) is Chowla's function, cf. A048050.

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

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

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

Cf. A048050, A002808.

Sequence in context: A336817 A340858 A309364 * A154925 A154962 A091655

Adjacent sequences: A062822 A062823 A062824 * A062826 A062827 A062828

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