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%I #9 Feb 24 2024 15:13:44
%S 1,3,10,15,28,45,78,105,153,190,253,300,325,435,465,528,595,630,780,
%T 903,1128,1275,1830,2145,2415,2485,2628,3160,3403,3570,3655,3828,4095,
%U 4753,4950,5050,5253,5460,5995,6105,6670,7503,8515,9180,9453,9730,10440,11175
%N Intersection of A000217 and A005098.
%C Triangular numbers T(m)=m(m+1)/2 indices m of which are in A027861. T(m) such that m^2+(m+1)^2 is prime.
%F a(n) = A027861(n)*(A027861(n)+1)/2.
%F a(n) = A000217(A027861(n)).
%p select(x-> isprime(4*x+1), [i*(i+1)/2$i=0..400])[]; # _Alois P. Heinz_, Feb 24 2024
%t Select[Table[n(n+1)/2, {n, 0, 200}], PrimeQ[4#+1]&] (* _Jean-François Alcover_, Feb 24 2024 *)
%Y Cf. A000217, A005098, A027861.
%K nonn
%O 1,2
%A _Zak Seidov_, May 26 2007
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