First 11 values of A121387 coincide with apparently unrelated new seq
Ray Chandler
rayjchandler at sbcglobal.net
Wed Jun 20 22:44:14 CEST 2007
I agree with Ralf that A121387 is Products of two primes of form 4n+1.
Consider the array:
Row 1 = A002145 Primes of the form 4n+3
Row 2 = A002144 Primes of the form 4n+1
Row 3 = A107978 Products of two primes of form 4n+3
Row 4 = A080774 Numbers with two prime factors: (4*i+1)*(4*j+3). Also semiprimes of the form 4n+3.
Row 5 = A121387 Products of two primes of form 4n+1
Note that union of A107978 and A121387 is A108181 semiprimes of form 4n+1.
The next four rows are odd 3-almost primes:
Row 6 Products of three primes of form 4n+3
Row 7 Numbers of form (4i+3)(4j+3)(4k+1)
Row 8 Numbers of form (4i+3)(4j+1)(4k+1)
Row 9 Products of three primes of form 4n+1
and so on.
The triangle resulting from reading the array by antidiagonals is A121388.
Ray Chandler
More information about the SeqFan
mailing list