0,1

A002387(n+1) < A000001(n) < A016088(n).

a(n) is the k-th semiprime: 1,13,262,10521,1034924&316108902 and factors: 2*2, 5*7, 13*61, 23*1879, 3*1765541 & 2*1005891739.

for a(1) s=1.0256943709884886355

for a(2) s=2.0009202082073190427...

for a(3) s=3.0000002945465013189...

for a(4) s=4.0000000316857024321...

for a(5) s=5.0000000001698140071...

a(0)=4 because 1/4>0.

a(1)=35 because 1/4+1/6+1/9+1/10+1/14+1/15+1/21+1/22+1/25+1/26+1/33+1/34+1/35 = 15708817/15315300 > 1.

s = 0; k = 1; Do[ While[s <= n, If[ Plus @@ Last /@ FactorInteger@k == 2, s = N[ s + 1/k, 20]]; k++ ]; Print[{k - 1, s}]; k ++, {n, 0, 5}]

Cf. A002387, A016088.

Sequence in context: A007134 A125798 A129581 this_sequence A076818 A005026 A123745

Adjacent sequences: A120052 A120053 A120054 this_sequence A120056 A120057 A120058

nonn

Jonathan Vos Post (jvospost3(AT)gmail.com) and Robert G. Wilson v (rgwv(AT)rgwv.com), Mar 25 2006