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A161678 Sum of c mod k for k from (smallest prime factor of c) to (largest prime factor of c) where c is composite(n). 0
0, 0, 0, 0, 3, 0, 10, 3, 0, 0, 2, 5, 22, 0, 0, 34, 0, 8, 2, 0, 22, 61, 5, 0, 77, 42, 1, 4, 26, 1, 105, 0, 0, 4, 59, 35, 0, 20, 5, 65, 172, 0, 207, 9, 0, 30, 17, 66, 123, 7, 0, 290, 3, 82, 17, 33, 2, 0, 343, 4, 48, 384, 197, 27, 2, 15, 99, 201, 470, 94, 0, 9, 23, 1, 61, 36, 4, 573, 0 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,5

COMMENTS

"composite(n)" stands for "n-th composite number", so composite(1) to composite(8) are 4, 6, 8, 9, 10, 12, 14, 15.

LINKS

Table of n, a(n) for n=1..79.

EXAMPLE

composite(2) = 6; (smallest prime factor of 6) = 2, (largest prime factor of 6) = 3. Hence a(2) = (6 mod 2)+(6 mod 3) = 0+0 = 0.

composite(5) = 10; (smallest prime factor of 10) = 2, (largest prime factor of 10) = 5. Hence a(5) = (10 mod 2)+(10 mod 3)+(10 mod 4)+(10 mod 5) = 0+1+2+0 = 3.

composite(7) = 14; (smallest prime factor of 14) = 2, (largest prime factor of 14) = 7. Hence a(7) = (14 mod 2)+(14 mod 3)+(14 mod 4)+(14 mod 5)+(14 mod 6)+(14 mod 7) = 0+2+2+4+2+0 = 10.

PROG

(MAGMA) [ &+[ n mod k: k in [D[1]..D[ #D]] where D is PrimeDivisors(n) ]: n in [4..110] | not IsPrime(n) ]; // Klaus Brockhaus, Jun 24 2009

CROSSREFS

Cf. A002808 (composite numbers), A004125 (sum of n mod k for k=1..n), A161517 (sum of c mod k for k=1..c where c is composite(n)).

Sequence in context: A138364 A095364 A094052 * A232267 A293939 A342926

Adjacent sequences:  A161675 A161676 A161677 * A161679 A161680 A161681

KEYWORD

nonn

AUTHOR

Juri-Stepan Gerasimov, Jun 16 2009

EXTENSIONS

Edited, corrected (a(22)=63 replaced by 61, a(25)=78 replaced by 77) and extended by Klaus Brockhaus, Jun 24 2009

STATUS

approved

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Last modified October 26 11:59 EDT 2021. Contains 348267 sequences. (Running on oeis4.)