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A089389 Sum of the smallest and the largest nontrivial divisor of n or 0 if n is 1 or a prime. 1
0, 0, 0, 4, 0, 5, 0, 6, 6, 7, 0, 8, 0, 9, 8, 10, 0, 11, 0, 12, 10, 13, 0, 14, 10, 15, 12, 16, 0, 17, 0, 18, 14, 19, 12, 20, 0, 21, 16, 22, 0, 23, 0, 24, 18, 25, 0, 26, 14, 27, 20, 28, 0, 29, 16, 30, 22, 31, 0, 32, 0, 33, 24, 34, 18, 35, 0, 36, 26, 37, 0, 38, 0, 39, 28, 40, 18, 41, 0, 42 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,4

COMMENTS

The product of the smallest and the largest nontrivial divisor is n. a(2m) = m+2, m >1.

LINKS

Antti Karttunen, Table of n, a(n) for n = 1..65537

FORMULA

a(1) = 0, for n > 1, if n is prime, a(n) = 0, otherwise a(n) = A020639(n) + A032742(n). - Antti Karttunen, Feb 25 2018

MATHEMATICA

Array[If[Or[# == 1, PrimeQ@ #], 0, #[[2]] + #[[-2]] &@ Divisors@ #] &, 80] (* Michael De Vlieger, Feb 25 2018 *)

PROG

(PARI)

A020639(n) = if(1==n, n, vecmin(factor(n)[, 1])); \\ From A020639.

A089389(n) = {my(spf=A020639(n)); if((1==n)||isprime(n), 0, spf+(n/spf)); }; \\ Antti Karttunen, Feb 25 2018

(Scheme) (define (A089389 n) (if (or (= 1 n) (= 1 (A010051 n))) 0 (+ (A020639 n) (A032742 n)))) ;; Antti Karttunen, Feb 25 2018

CROSSREFS

Cf. A020639, A032742.

Sequence in context: A055241 A055242 A200295 * A081550 A046779 A255369

Adjacent sequences:  A089386 A089387 A089388 * A089390 A089391 A089392

KEYWORD

easy,nonn

AUTHOR

Amarnath Murthy, Nov 10 2003

EXTENSIONS

More terms from David Wasserman, Sep 15 2005

STATUS

approved

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Last modified August 20 03:48 EDT 2019. Contains 326139 sequences. (Running on oeis4.)