OFFSET
1,1
FORMULA
sp(n)+sp(n+1)=q^2, sp(n)=n-th semiprime.
EXAMPLE
6 is ok because sp(6)=15, sp(7)=21, 15+21=36=6^2, sp(n)=A001358(n)=n-th semiprime.
MATHEMATICA
Position[Partition[Select[Range[40000], PrimeOmega[#]==2&], 2, 1], _?(IntegerQ[ Sqrt[Total[#]]]&), 1, Heads->False]//Flatten (* Harvey P. Dale, Jul 05 2018 *)
PROG
(PARI) lista(nn) = {vec = vector(nn, i, i); sp = select(i->(bigomega(i)==2), vec); for (i = 1, #sp-1, if (issquare(sp[i+1]+sp[i]), print1(i, ", ")); ); } \\ Michel Marcus, Oct 06 2013
CROSSREFS
KEYWORD
nonn
AUTHOR
Zak Seidov, Jun 27 2005
EXTENSIONS
More terms from Michel Marcus, Oct 06 2013
STATUS
approved