A101303 a(n) = sigma() [A000203] applied n times to prime(n).

3, 7, 28, 60, 360, 1512, 3276, 16256, 65528, 261120, 79360, 1098240, 13852800, 25261824, 79536128, 1040179456, 1710858240, 13815410400, 71687577600, 137707384824, 151060010112, 1932916285440, 4212741841200, 508764077015040, 24560669041920, 26379664917984

Offset: 1

Author

Jorge Coveiro, Dec 22 2004

Keywords

• nonn
• easy

Examples

			a(1)=  3 = sigma(2);
a(2)=  7 = sigma(sigma(3));
a(3)= 28 = sigma(sigma(sigma(5)));
a(4)= 60 = sigma(sigma(sigma(sigma(7)))).
		

Crossrefs

Cf. A000203, A090896.

Programs

Maple

a:= n-> (numtheory[sigma]@@n)(ithprime(n)):
seq(a(n), n=1..30);  # Alois P. Heinz, Oct 03 2018

Mathematica

f[n_] := DivisorSigma[1, n]; Table[ Nest[f, Prime[n], n], {n, 25}] (* Robert G. Wilson v, Dec 22 2004 *)

Extensions

Edited and extended by Robert G. Wilson v, Dec 22 2004