login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A283530 The number of reduced phi-partitions of n. 4

%I #26 Oct 27 2023 20:49:43

%S 0,0,1,1,1,0,1,2,1,1,1,1,1,2,2,3,1,1,1,2,3,3,1,1,2,3,3,3,1,0,1,5,4,4,

%T 3,2,1,5,4,4,1,1,1,6,6,7,1,3,2,6,5,8,1,3,4,8,6,10,1,1,1,11,9,12,5,2,1,

%U 12,8,5,1,5,1,14,13,14,5,3,1,13,9,16,1,1

%N The number of reduced phi-partitions of n.

%C The reduced phi-partitions of n are partitions n= a_1 +a_2 +a_3 +... +a_k into at least 2 parts such that each part is simple (i.e. each part in A002110, as required in A283529) and such that in addition phi(n) = sum_i phi(a_i), as required in A283528. phi(.) = A000010(.) is Euler's totient.

%C Numbers n where a(n)=1 are called semisimple. 3, 4, 5, 7, 9, 10, 11, 12, 13, 17, 18, 19, 23, 24,... are semisimple (see A283320). In this list of semisimple numbers there are no odd numbers besides 9 and the odd primes.

%H Alois P. Heinz, <a href="/A283530/b283530.txt">Table of n, a(n) for n = 1..10000</a> (first 1000 terms from Giovanni Resta)

%H J. Wang, <a href="http://www.fq.math.ca/Scanned/31-4/wang.pdf">Reduced phi-partitions of positive integers</a>, Fib. Quart. 31 (4) (1993) 365-369.

%H J. Wang, X. Wang, <a href="http://www.fq.math.ca/Papers1/44-2/quartwang02_2006.pdf">On the set of reduced phi-partitions of a positive integer</a>, Fib. Quart. 44 (2) (2006) 98-102.

%F a(A002110(k)) = 0. [Wang]

%e a(15)=2 counts 1+2+2+2+2+2+2= 1+1+1+2+2+2+6.

%e a(16)=3 counts 2+2+2+2+2+2+2+2 = 1+1+2+2+2+2+6 = 1+1+1+1+6+6.

%p isA002110 := proc(n)

%p member(n,[1, 2, 6, 30, 210, 2310, 30030, 510510, 9699690, 223092870, 6469693230, 200560490130, 7420738134810, 304250263527210, 13082761331670030, 614889782588491410, 32589158477190044730, 1922760350154212639070]) ;

%p end proc:

%p A283530 := proc(n)

%p local a,k,issimp,p ;

%p a := 0 ;

%p for k in combinat[partition](n) do

%p issimp := true ;

%p for p in k do

%p if not isA002110(p) then

%p issimp := false;

%p break;

%p end if;

%p end do:

%p if issimp and nops(k) > 1 then

%p phip := add(numtheory[phi](p),p=k) ;

%p if phip = numtheory[phi](n) then

%p a := a+1 ;

%p end if;

%p end if;

%p end do:

%p a ;

%p end proc:

%t v={1,2,6,30,210}; e=10^9 v + EulerPhi@v; a[n_] := Length@ IntegerPartitions[ 10^9 n + EulerPhi[n], {2, Infinity}, e]; Array[a, 100] (* suitable for n <= 1000, _Giovanni Resta_, Mar 10 2017 *)

%Y Cf. A283528, A283529, A283320.

%K nonn

%O 1,8

%A _R. J. Mathar_, Mar 10 2017

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified March 28 10:55 EDT 2024. Contains 371241 sequences. (Running on oeis4.)