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A113492 Least integers, starting with 1, so ascending descending base exponent transforms all triprimes. 2
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified February 25 00:39 EST 2018. Contains 299630 sequences. (Running on oeis4.)