OFFSET
1,2
COMMENTS
Each term is the sum of two oblong numbers and therefore even.
EXAMPLE
a(1)=0 from x=y=1, with 2 a prime.
a(2)=2 from x=1, y=2, with 5 a prime.
a(3)=8 from x=2, y=3, with 13 a prime.
a(4)=12 from x=1, y=4, with 17 a prime.
a(4)=22 from x=2, y=5, with 29 a prime.
a(.)=212 from x=2, y=15, with 229 a prime, or from x=8, y=13, with 233 a prime.
MAPLE
obl := proc(n) n*(n-1) ; end: lim := 800; L := {} ;
for x from 0 to lim/2 do for y from x to lim/2 do if obl(x)+obl(y) <= lim then if isprime(x^2+y^2) then L := L union { obl(x)+obl(y) } ; fi; fi; od: od: sort(L) ; # R. J. Mathar, Sep 11 2009
MATHEMATICA
Take[#[[1]](#[[1]]-1)+#[[2]](#[[2]]-1)&/@Select[Tuples[ Range[ 0, 40], 2], PrimeQ[ Total[#^2]]&]//Union, 60] (* Harvey P. Dale, Jun 07 2020 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Juri-Stepan Gerasimov, Jun 26 2009, Jul 29 2009
EXTENSIONS
Duplicates of 212 and 432 removed, 500 removed by R. J. Mathar, Sep 11 2009
STATUS
approved