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

1,2

Comments

This is the triprime analogy to A113320.

Links

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

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}.

Example

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

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 *)

Crossrefs

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

Sequence in context: A213671 A050081 A144076 * A097152 A212769 A269485

Adjacent sequences: A113489 A113490 A113491 * A113493 A113494 A113495

Keyword

easy,nonn

Author

Jonathan Vos Post, Jan 10 2006

Extensions

Corrected and extended by Giovanni Resta, Jun 13 2016

Status

approved