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A283530 The number of reduced phi-partitions of n. 4
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, 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, 12, 8, 5, 1, 5, 1, 14, 13, 14, 5, 3, 1, 13, 9, 16, 1, 1 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,8
COMMENTS
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.
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.
LINKS
Alois P. Heinz, Table of n, a(n) for n = 1..10000 (first 1000 terms from Giovanni Resta)
J. Wang, Reduced phi-partitions of positive integers, Fib. Quart. 31 (4) (1993) 365-369.
J. Wang, X. Wang, On the set of reduced phi-partitions of a positive integer, Fib. Quart. 44 (2) (2006) 98-102.
FORMULA
a(A002110(k)) = 0. [Wang]
EXAMPLE
a(15)=2 counts 1+2+2+2+2+2+2= 1+1+1+2+2+2+6.
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.
MAPLE
isA002110 := proc(n)
member(n, [1, 2, 6, 30, 210, 2310, 30030, 510510, 9699690, 223092870, 6469693230, 200560490130, 7420738134810, 304250263527210, 13082761331670030, 614889782588491410, 32589158477190044730, 1922760350154212639070]) ;
end proc:
A283530 := proc(n)
local a, k, issimp, p ;
a := 0 ;
for k in combinat[partition](n) do
issimp := true ;
for p in k do
if not isA002110(p) then
issimp := false;
break;
end if;
end do:
if issimp and nops(k) > 1 then
phip := add(numtheory[phi](p), p=k) ;
if phip = numtheory[phi](n) then
a := a+1 ;
end if;
end if;
end do:
a ;
end proc:
MATHEMATICA
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 *)
CROSSREFS
Sequence in context: A236859 A278401 A069935 * A326753 A062093 A177457
KEYWORD
nonn
AUTHOR
R. J. Mathar, Mar 10 2017
STATUS
approved

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Last modified March 28 18:04 EDT 2024. Contains 371254 sequences. (Running on oeis4.)