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A071189 Smallest prime factor of sum of divisors of n. 6
1, 3, 2, 7, 2, 2, 2, 3, 13, 2, 2, 2, 2, 2, 2, 31, 2, 3, 2, 2, 2, 2, 2, 2, 31, 2, 2, 2, 2, 2, 2, 3, 2, 2, 2, 7, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 3, 3, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 127, 2, 2, 2, 2, 2, 2, 2, 3, 2, 2, 2, 2, 2, 2, 2, 2, 11, 2, 2, 2, 2, 2, 2, 2 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Antti Karttunen, Table of n, a(n) for n = 1..10000

FORMULA

a(n) = A020639(A000203(n)).

MATHEMATICA

Table[FactorInteger[DivisorSigma[1, n]][[1, 1]], {n, 90}] (* Harvey P. Dale, May 15 2011 *)

PROG

(PARI) A071189(n) = if(1==n, n, my(f = factor(sigma(n))); vecmin(f[, 1])); \\ Antti Karttunen, Jul 24 2017

(PARI) first(n) = {my(v = vector(n, i, 2), sq = List()); for(i=1, sqrtint(n), listput(sq, i^2); listput(sq, 2*i^2)); listsort(sq); v[1]=1; for(i=2, #sq, if(sq[i]>n, break); v[sq[i]] = factor(sigma(sq[i]))[, 1]~[1]); v} \\ David A. Corneth, Jul 24 2017

CROSSREFS

Cf. A000203, A020639, A028982, A071187, A071190.

Sequence in context: A085594 A085587 A326607 * A137822 A300845 A302714

Adjacent sequences:  A071186 A071187 A071188 * A071190 A071191 A071192

KEYWORD

nonn

AUTHOR

Reinhard Zumkeller, May 15 2002

STATUS

approved

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Last modified February 29 08:26 EST 2020. Contains 332355 sequences. (Running on oeis4.)