A320877 - OEIS

A320877

a(n) = 1 + Sum_{k=1..n} 2^prime(k).

1, 5, 13, 45, 173, 2221, 10413, 141485, 665773, 9054381, 545925293, 2693408941, 140132362413, 2339155617965, 11135248640173, 151872736995501, 9159071991736493, 585619824295159981, 2891462833508853933, 150465415423185266861, 2511648656858007873709, 11956381622597298301101

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OFFSET

0,2

COMMENTS

Indices of noncomposite terms are 0, 1, 2, 4, 5, 8, 43, 127, 251, ...

LINKS

Table of n, a(n) for n=0..21.

FORMULA

a(n) = A076793(n) + 1.

MATHEMATICA

Join[{1}, Accumulate[2^Prime[Range[30]]]+1] (* Harvey P. Dale, Mar 26 2019 *)

PROG