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A141554 Transformed nonprime products of prime factors of the composites, the largest prime decremented by 2 and the smallest prime incremented by 2. 1
0, 4, 0, 12, 8, 20, 15, 0, 12, 24, 25, 36, 16, 21, 44, 15, 40, 36, 0, 45, 60, 35, 24, 68, 55, 48, 60, 72, 45, 84, 32, 45, 60, 75, 88, 36, 63, 80, 85, 108, 72, 116, 75, 0, 77, 108, 120, 105, 100, 48, 140, 75, 136, 81, 132, 96, 45, 156, 120, 105, 164, 135, 144, 108, 99, 168 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

In the prime number decomposition of k=A002808(i), i=1,2,3,.., one instance of the largest prime, pmax=A052369(i), is replaced by pmax-2 and one instance of the smallest prime, pmin=A056608(i), is replaced by pmin+2. If the product of this modified list of factors, k*(pmax-2)*(pmin+2)/(pmin*pmax), is nonprime, it is added to the sequence.

LINKS

Table of n, a(n) for n=1..66.

EXAMPLE

k(1)=4=(p(max)=2)*(p(min)=2), transformed (2-2)*(2+2)=0*4=0=a(1).

k(2)=6=(p(max)=3)*(p(min)=2), transformed (3-2)*(2+2)=1*4=4=a(2).

k(3)=8=(p(max)=2)*(p=2)*(p(min)=2), transformed (2-2)*2*(2+2)=0*2*4=0=a(3).

k(4)=9=(p(max)=3)*(p(min)=3), transformed (3-2)*(3+2)=1*5=5 (prime, skipped).

k(5)=10=(p(max)=5)*(p(min)=2), transformed (5-2)*(2+2)=3*4=12=a(4).

CROSSREFS

Cf. A141218, A141219, A141220, A141284.

Sequence in context: A273761 A273424 A273329 * A076600 A002978 A273609

Adjacent sequences:  A141551 A141552 A141553 * A141555 A141556 A141557

KEYWORD

nonn

AUTHOR

Juri-Stepan Gerasimov, Aug 14 2008

EXTENSIONS

Edited and corrected by R. J. Mathar, Aug 18 2008

STATUS

approved

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Last modified August 7 17:44 EDT 2020. Contains 336278 sequences. (Running on oeis4.)