A196152 - OEIS

A196152

a(n) = Sum_{j=1..n} c(j)^c(n+1-j) where c(k) is the k-th composite number.

256, 5392, 116288, 2210465, 28444929, 255528577, 4009404505, 153081728914, 5171603025026, 62036152111810, 699273704703624, 25869244015854483, 1361620781025221899, 22882871550589429987, 317257878688421267438, 11004311280566297309676, 258894081066969988746661

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OFFSET

1,1

COMMENTS

For n smaller than 100, a(n) can be approximated by exp(0.0075*n^2 + 3.0857*n - 0.166).

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 1..200

FORMULA

a(n) = Sum_{j=1..n} A002808(j)^A002808(n+1-j).

EXAMPLE

For n = 4, a(4) = 4^9 + 6^8 + 8^6 + 9^4 = 2210465.

MATHEMATICA

Composite[n_Integer] := FixedPoint[n + PrimePi[#] + 1&, n]; Table[Sum[Composite[j]^Composite[i+1-j], {j, i}], {i, 10}]

PROG

(PARI) iscomposite(n) = if (n==1, 0, !isprime(n));

a(n) = {vc = []; ic = 1; while (#vc != n, if (iscomposite(ic), vc = concat(vc, ic)); ic++); sum(i=1, n, vc[i]^vc[n+1-i]); } \\ Michel Marcus, Aug 06 2014

CROSSREFS

Cf. A002808.

Sequence in context: A115111 A200790 A206110 * A113173 A223964 A195595

Adjacent sequences: A196149 A196150 A196151 * A196153 A196154 A196155

KEYWORD

nonn

AUTHOR

Josh Kirklin, Sep 28 2011

STATUS

approved