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A031126 Number of proper factorizations of p1^n*p2^3, where p1 and p2 are distinct primes. 1
2, 6, 15, 30, 56, 96, 161, 256, 400, 607, 906, 1324, 1913, 2718, 3823, 5312, 7315, 9972, 13494, 18104, 24131, 31937, 42020, 54947, 71483, 92491, 119119, 152685, 194886, 247692, 313612, 395546, 497153, 622687, 777423, 967524, 1200571 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,1
LINKS
FORMULA
a(n) = A000412(n) - 1 = A028422(2^n*3^3). - Ray Chandler, May 01 2017
EXAMPLE
a(0)=2 since 2^3=8 has two proper (i.e. nontrivial) factorizations, 2*4 and 2*2*2. a(1)=6 since 2*3^3 = 54 has the proper factorizations 2*27, 2*3*9, 2*3*3*3, 6*3*3, 6*9, 18*3. - N. J. A. Sloane, May 01 2017
CROSSREFS
Sequence in context: A342163 A098651 A087427 * A289373 A289102 A289402
KEYWORD
nonn
AUTHOR
EXTENSIONS
Offset changed to 0 and more terms added by Ray Chandler, May 01 2017
STATUS
approved

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Last modified February 29 11:59 EST 2024. Contains 370425 sequences. (Running on oeis4.)