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A277240 Number of factorizations of m^n into exactly four factors, where m is a product of two distinct primes. 2
1, 2, 9, 27, 74, 168, 363, 703, 1297, 2247, 3742, 5967, 9241, 13859, 20307, 29052, 40786, 56187, 76233, 101858, 134377, 175068, 225640, 287772, 363673, 455482, 565977, 697875, 854594, 1039500, 1256787, 1510547, 1805833, 2147607, 2541870, 2994543, 3512737 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

Alois P. Heinz, Table of n, a(n) for n = 0..10000

Index entries for linear recurrences with constant coefficients, signature (2,1,-2,-2,-2,5,2,0,-2,-5,2,2,2,-1,-2,1)

FORMULA

G.f.: -(x^12 +4*x^10 +9*x^9 +17*x^8 +17*x^7 +24*x^6 +17*x^5 +17*x^4 +9*x^3 +4*x^2 +1) / ((x^2+1) *(x^2+x+1)^2 *(x+1)^3 *(x-1)^7).

EXAMPLE

a(2) = 9: (2*3)^2 = 2*2*3*3 = 1*3*3*4 = 1*2*3*6 = 1*2*2*9 = 1*1*4*9 = 1*1*6*6 = 1*1*2*18 = 1*1*3*12 = 1*1*1*36.

CROSSREFS

Column k=4 of A277239.

Sequence in context: A239059 A153977 A051746 * A256233 A123904 A019065

Adjacent sequences:  A277237 A277238 A277239 * A277241 A277242 A277243

KEYWORD

nonn

AUTHOR

Alois P. Heinz, Oct 06 2016

STATUS

approved

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Last modified July 20 16:15 EDT 2019. Contains 325185 sequences. (Running on oeis4.)