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A030628 1 together with numbers of the form p*q^4 and p^9, where p and q are primes. 12


%S 1,48,80,112,162,176,208,272,304,368,405,464,496,512,567,592,656,688,

%T 752,848,891,944,976,1053,1072,1136,1168,1250,1264,1328,1377,1424,

%U 1539,1552,1616,1648,1712,1744,1808,1863,1875,2032,2096,2192,2224,2349,2384

%N 1 together with numbers of the form p*q^4 and p^9, where p and q are primes.

%C Also 1 together with numbers with 10 divisors. Also numbers n such that product of all proper divisors of n equals n^4.

%C If M(n) denotes the product of all divisors of n, then n is said to be k-multiplicatively perfect if M(n)=n^k. All such numbers are of the form p*q^(k-1) or p^(2k-1). The sequence A030628 is therefore 5-multiplicatively perfect. See the Links for A007422. - _Walter Kehowski_, Sep 13 2005

%D D. M. Burton, Elementary Number Theory, Allyn and Bacon Inc., Boston, MA, 1976. p. 119.

%D David Wells, The Penguin Dictionary of Curious and Interesting Numbers, entry for 48, page 106, 1997.

%H R. J. Mathar, <a href="/A030628/b030628.txt">Table of n, a(n) for n = 1..1000</a>

%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/DivisorProduct.html">Divisor Product</a>

%F Union A178739 U A179665 {1}. - _R. J. Mathar_, Apr 03 2011

%p with(numtheory): k:=5: MPL:=[]: for z from 1 to 1 do for n from 1 to 5000 do if convert(divisors(n),`*`) = n^k then MPL:=[op(MPL),n] fi od; od; MPL; # _Walter Kehowski_, Sep 13 2005

%t Join[{1},Select[Range[6000],DivisorSigma[0,#]==10&]] (* _Vladimir Joseph Stephan Orlovsky_, May 05 2011 *)

%o (PARI) {v=[]; for(n=1,500,v=concat(v, if(numdiv(n)==10,n,",")); ); v} \\ _Jason Earls_, Jun 18 2001

%o (PARI) list(lim)=my(v=List([1]), t); forprime(p=2, (lim\2+.5)^(1/4), t=p^4; forprime(q=2, lim\t, if(p==q, next); listput(v, t*q))); forprime(p=2,(lim+.5)^(1/9),listput(v,p^9)); vecsort(Vec(v)) \\ _Charles R Greathouse IV_, Apr 26 2012

%Y Cf. A030515, A030627, A030629.

%K nonn,easy,nice

%O 1,2

%A _Jeff Burch_

%E Better description from Sharon Sela (sharonsela(AT)hotmail.com), Dec 23 2001

%E More terms from _Walter Kehowski_, Sep 13 2005

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Last modified May 26 17:40 EDT 2020. Contains 334630 sequences. (Running on oeis4.)