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A189803 Composite numbers n such that n'' = n'-1 where n' and n'' are the first and the second arithmetic derivative of n. 0
9, 185, 341, 377, 437, 9005, 30413, 33953, 41009, 51533, 82673, 92909, 103073, 126509, 143009, 165773, 181793, 184973, 191309, 228653, 231713, 246893, 291233, 311309, 316973, 319793, 329357, 353009, 358433, 374513, 398093, 405809, 431009, 460193, 467309 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The sequence A189710 (n"=n'-1) includes all prime numbers because p'=1 and p" = 0. Composite numbers are not very frequent.

Are all terms semiprimes? These terms appear to be p*q such that p+q is a term in A054377, which has solutions to the equation n' = n-1. - T. D. Noe, Apr 27 2011

LINKS

Table of n, a(n) for n=1..35.

EXAMPLE

9' = 6, 9''= 6'= 5, 9" = 9'- 1 -> 9 is in the sequence.

CROSSREFS

Cf. A003415, A054377, A189710.

Sequence in context: A064332 A319798 A300598 * A216409 A171194 A196297

Adjacent sequences:  A189800 A189801 A189802 * A189804 A189805 A189806

KEYWORD

nonn

AUTHOR

Giorgio Balzarotti, Apr 27 2011

STATUS

approved

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Last modified September 23 11:23 EDT 2020. Contains 337310 sequences. (Running on oeis4.)