1,1

a(1) = 5 because prime 5 divides 275 = numerator[1/2^5 + 1/3^5].

Sum[1/Prime[k]^Prime[n],{k,1,n-1}] begins

n=2 1/2^3 = 1/8

n=3 1/2^5 + 1/3^5 = 275/7776

n=4 1/2^7 + 1/3^7 + 1/5^7 = 181139311/21870000000

n=5 1/2^11 + 1/3^11 + 1/5^11 + 1/7^11 = 17301861338484245234233/35027750054222100000000000

Cf. A119722.

Sequence in context: A094465 A020580 A045458 this_sequence A024191 A100104 A015650

Adjacent sequences: A120286 A120287 A120288 this_sequence A120290 A120291 A120292

frac,nonn

Alexander Adamchuk (alex(AT)kolmogorov.com), Jul 08 2006