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A129307
Intersection of A000217 and A005098.
7
1, 3, 10, 15, 28, 45, 78, 105, 153, 190, 253, 300, 325, 435, 465, 528, 595, 630, 780, 903, 1128, 1275, 1830, 2145, 2415, 2485, 2628, 3160, 3403, 3570, 3655, 3828, 4095, 4753, 4950, 5050, 5253, 5460, 5995, 6105, 6670, 7503, 8515, 9180, 9453, 9730, 10440, 11175
OFFSET
1,2
COMMENTS
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.
FORMULA
a(n) = A027861(n)*(A027861(n)+1)/2.
a(n) = A000217(A027861(n)).
MAPLE
select(x-> isprime(4*x+1), [i*(i+1)/2$i=0..400])[]; # Alois P. Heinz, Feb 24 2024
MATHEMATICA
Select[Table[n(n+1)/2, {n, 0, 200}], PrimeQ[4#+1]&] (* Jean-François Alcover, Feb 24 2024 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Zak Seidov, May 26 2007
STATUS
approved