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

Author

Jason Earls, Jul 20 2001

Keywords

• nonn
• look
• easy

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

Crossrefs

Cf. A048050, A002808.

Programs

Haskell

a062825 1 = 0
a062825 n = sum $ a163870_row (n - 1) -- Reinhard Zumkeller, Mar 29 2014

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 *)

PARI

j=[0]; for(n=2,200, if(isprime(n), n+1,j=concat(j, sigma(n)-n-1))); j

Extensions

Definition revised and a(1) corrected by Reinhard Zumkeller, Mar 29 2014