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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 (list; graph; refs; listen; history; text; internal format)
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-Fran├žois 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: A305210 A165501 A274614 * 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

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Last modified May 25 03:14 EDT 2019. Contains 323539 sequences. (Running on oeis4.)