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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

Giovanni Resta and 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

Cf. A283528, A283529, A283320.

Sequence in context: A236859 A278401 A069935 * A326753 A062093 A177457

Adjacent sequences:  A283527 A283528 A283529 * A283531 A283532 A283533

KEYWORD

nonn

AUTHOR

R. J. Mathar, Mar 10 2017

STATUS

approved

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Last modified January 23 04:16 EST 2020. Contains 331168 sequences. (Running on oeis4.)