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A327901
Nonprime squarefree numbers whose prime indices all have the same sum of prime indices (A056239).
3
1, 35, 143, 209, 247, 391, 493, 629, 667, 851, 901, 1073, 1219, 1333, 1457, 1537, 1891, 1961, 2021, 2201, 2623, 2717, 2759, 2867, 2993, 3053, 3239, 3337, 3827, 3977, 4061, 4183, 4223, 4331, 4387, 4633, 5429, 5633, 5767, 5959, 6157, 6191, 6319, 7081, 7093, 7519
OFFSET
1,2
COMMENTS
A prime index of n is a number m such that prime(m) divides n. The multiset of prime indices of n is row n of A112798.
EXAMPLE
The sequence of terms together with their prime indices begins:
1: {}
35: {3,4}
143: {5,6}
209: {5,8}
247: {6,8}
391: {7,9}
493: {7,10}
629: {7,12}
667: {9,10}
851: {9,12}
901: {7,16}
1073: {10,12}
1219: {9,16}
1333: {11,14}
1457: {11,15}
1537: {10,16}
1891: {11,18}
1961: {12,16}
2021: {14,15}
2201: {11,20}
MATHEMATICA
primeMS[n_]:=If[n==1, {}, Flatten[Cases[FactorInteger[n], {p_, k_}:>Table[PrimePi[p], {k}]]]];
Select[Range[1000], !PrimeQ[#]&&SquareFreeQ[#]&&SameQ@@Total/@primeMS/@primeMS[#]&];
CROSSREFS
The version including primes and nonsquarefree numbers is A326534.
The version for number of prime indices is A327900.
The version for mean of prime indices is A327902.
Sequence in context: A157286 A354543 A324072 * A346910 A290560 A136017
KEYWORD
nonn
AUTHOR
Gus Wiseman, Sep 30 2019
STATUS
approved