A113492 Least integers, starting with 1, so ascending descending base exponent transforms all triprimes.

1, 7, 11, 3, 3, 4, 3, 5, 11, 4, 1, 2, 1, 1, 4, 8, 8, 2, 2, 6, 6, 7, 7, 3, 1, 3, 4, 2, 7, 2, 2, 3, 2, 2, 4, 1, 3, 12, 5, 2, 2, 1, 3, 5, 3, 4, 4, 4, 14, 2, 1, 2, 11, 4, 6, 2, 1, 2, 7, 8, 4, 6, 1, 3, 1, 8, 1, 2, 4, 3, 12, 8, 1, 2, 11, 1, 2, 10, 2, 3, 3, 9, 1, 1

Offset: 1

Author

Jonathan Vos Post, Jan 10 2006

Keywords

• easy
• nonn

Comments

This is the triprime analogy to A113320.

Examples

			a(1) = 1 by definition.
a(2) = 7 because 1^7 + 7^1 = 8 = 2^3 is a triprime (A014612).
		

Links

• G. C. Greubel, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A014612, A113320, A005408, A113122, A113153, A113154, A113336, A113271, A113258, A113257, A113231, A087316, A113208.

Programs

Mathematica

p3[n_] := PrimeOmega[n] == 3; inve[w_] := Total[w^Reverse[w]]; a[1] = 1; a[n_] := a[n] = Block[{k = 0}, While[! p3[ inve@ Append[ Array[a, n - 1], ++k]]]; k]; Array[a, 75] (* Giovanni Resta, Jun 13 2016 *)

Formula

a(1) = 1. For n > 1: a(n) = min {n > 0: Sum_{i=1..n} a(i)^a(n-i+1) is a triprime}. a(n) = min {n > 0: Sum_{i=1..n} a(i)^a(n-i+1) in A014612}.

Extensions

Corrected and extended by Giovanni Resta, Jun 13 2016