

A108939


Triangle read by rows in which row n lists all primes p such that p1n.


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
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OFFSET

1,1


COMMENTS

Row 2n1 contains only the term 2.


LINKS

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


EXAMPLE

Row n = 1 : 2 because 11.
Row n = 2 : 2, 3 because 12 and 22.
Row n = 3 : 2 because 13.
Row n = 4 : 2, 3, 5 because 14, 24 and 44.
Row n = 5 : 2 because 15.
Row n = 6 : 2, 3, 7 because 16, 26 and 66.
Row n = 7 : 2 because 17.
Row n = 8 : 2, 3, 5 because 18, 28 and 48.
Row n = 9 : 2 because 19.
Row n = 10 : 2, 3, 11 because 110, 210 and 1010.
Row n = 11 : 2 because 111.
Row n = 12 : 2, 3, 5, 7, 13 because 112, 212, 412, 612 = and 1212.


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



