1,1

a(n) = A000217(i) = A007504(j) for appropriate i, j.

These are the 4, 7, 516, 2904, 328777, ... -th triangular numbers and are the sums of the first 3, 5, 217, 1065, 93448, ... prime numbers respectively.

a(2) = 28, as A000217(7) = 1+2+3+4+5+6+7 = 28 = 2+3+5+7+11 = A007504(5).

a066527(m) = local(d, ds, p, ps); d=1; ds=1; p=2; ps=2; while(ds<m, if(ds==ps, print1(ds, ", "); d++; ds=ds+d; p++; p=nextprime(p); ps=ps+p, if(ds<ps, d++; ds=ds+d, p++; p=nextprime(p); ps=ps+p))) a066527(10^11)

s = 0; Do[s = s + Prime[n]; t = Floor[ Sqrt[2*s]]; If[t*(t + 1) == 2s, Print[s]], {n, 1, 10^6} ]

Sequence in context: A076712 A116973 A003665 this_sequence A103423 A102542 A098751

Adjacent sequences: A066524 A066525 A066526 this_sequence A066528 A066529 A066530

nonn,nice,more

Reinhard Zumkeller (reinhard.zumkeller(AT)lhsystems.com), Jan 06, 2002

One more term from Klaus Brockhaus (klaus-brockhaus(AT)t-online.de) and Robert G. Wilson v (rgwv(AT)rgwv.com), Jan 07 2002

One more term from Philip Sung (philip_sung(AT)hotmail.com), Jan 25 2002