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A180114 Sigma(A001694(n)), sum of divisors of the powerful number A001694(n). 0
1, 7, 15, 13, 31, 31, 40, 63, 91, 57, 127, 195, 121, 217, 280, 133, 156, 255, 403, 183, 399, 465, 600, 403, 364, 511, 819, 307, 847, 400, 381, 855, 961, 1240, 741, 931, 1092, 1023, 553, 1651, 781, 1815, 1240, 1281, 1093, 1767, 1953, 871, 2520, 2821, 993, 1995 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Table of n, a(n) for n=1..52.

EXAMPLE

Sigma(2^2)=7, sigma(2^3)=15, sigma(3^2)=13.

MAPLE

emin := proc(n::posint) local L; if n>1 then L:=ifactors(n)[2]; L:=map(z->z[2], L); min(L) else 0 fi end: L:=[]: for w to 1 do for n from 1 to 144 do sn:=sigma(n); if emin(n)>1 then L:=[op(L), sn]; print(n, ifactor(n), sn, ifactor(sn)) fi; od; od;

MATHEMATICA

pwfQ[n_] := n == 1 || Min[Last /@ FactorInteger[n]] > 1; DivisorSigma[1, Select[ Range@ 1000, pwfQ]] (* Giovanni Resta, Feb 06 2018 *)

CROSSREFS

Cf. A001694, A000203, A180090, A180097, A180098.

Sequence in context: A290629 A234861 A076401 * A204740 A244536 A237054

Adjacent sequences:  A180111 A180112 A180113 * A180115 A180116 A180117

KEYWORD

easy,nonn

AUTHOR

Walter Kehowski, Aug 10 2010

EXTENSIONS

a(1)=1 prepended by and more terms from Giovanni Resta, Feb 06 2018

STATUS

approved

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Last modified August 18 18:19 EDT 2018. Contains 313834 sequences. (Running on oeis4.)