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A108939 Triangle read by rows in which row n lists all primes p such that p-1|n. 1
2, 2, 3, 2, 2, 3, 5, 2, 2, 3, 7, 2, 2, 3, 5, 2, 2, 3, 11, 2, 2, 3, 5, 7, 13, 2, 2, 3, 2, 2, 3, 5, 17, 2, 2, 3, 7, 19, 2, 2, 3, 5, 11, 2, 2, 3, 23, 2, 2, 3, 5, 7, 13, 2, 2, 3, 2, 2, 3, 5, 29, 2, 2, 3, 7, 11, 31, 2, 2, 3, 5, 17, 2, 2, 3, 2, 2, 3, 5, 7, 13, 19, 2, 2, 3, 2, 2, 3, 5, 11, 2, 2 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Row 2n-1 contains only the term 2.

LINKS

Table of n, a(n) for n=1..92.

EXAMPLE

Row n = 1 : 2 because 1|1.

Row n = 2 : 2, 3 because 1|2 and 2|2.

Row n = 3 : 2 because 1|3.

Row n = 4 : 2, 3, 5 because 1|4, 2|4 and 4|4.

Row n = 5 : 2 because 1|5.

Row n = 6 : 2, 3, 7 because 1|6, 2|6 and 6|6.

Row n = 7 : 2 because 1|7.

Row n = 8 : 2, 3, 5 because 1|8, 2|8 and 4|8.

Row n = 9 : 2 because 1|9.

Row n = 10 : 2, 3, 11 because 1|10, 2|10 and 10|10.

Row n = 11 : 2 because 1|11.

Row n = 12 : 2, 3, 5, 7, 13 because 1|12, 2|12, 4|12, 6|12 = and 12|12.

MAPLE

with(numtheory): for n from 1 to 20 do div:=divisors(n): A:=[seq(div[j]+1, j=1..tau(n))]: B:={}: for i from 1 to tau(n) do if isprime(A[i])=true then B:=B union {A[i]} else B:=B: fi: od: C:=convert(B, list): b[n]:=C: od: for n from 1 to 20 do b[n]:=b[n] od; # yields sequence in triangular form - Emeric Deutsch, Aug 03 2005

CROSSREFS

Row products are A027760. Row sums are A085020. Cf. A067513, A108077.

Sequence in context: A268672 A054483 A258568 * A138143 A285727 A281908

Adjacent sequences:  A108936 A108937 A108938 * A108940 A108941 A108942

KEYWORD

easy,nonn,tabf

AUTHOR

Philippe Deléham, Jul 20 2005

STATUS

approved

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Last modified May 19 02:45 EDT 2019. Contains 323377 sequences. (Running on oeis4.)