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A113433 Semi-Pierpont semiprimes: products of exactly two Pierpont primes A005109. 3
4, 6, 9, 10, 14, 15, 21, 25, 26, 34, 35, 38, 39, 49, 51, 57, 65, 74, 85, 91, 95, 111, 119, 133, 146, 169, 185, 194, 218, 219, 221, 247, 259, 289, 291, 323, 326, 327, 361, 365, 386, 481, 485, 489, 511, 514, 545, 579, 629, 679, 703, 763, 771, 815, 866, 949, 965 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Semiprime both of whose prime factors are Pierpont primes (A005109), which are primes of the form (2^K)*(3^L)+1. Not to be confused with A113432: Pierpont semiprimes [Semiprimes of the form (2^K)*(3^L)+1]. This terminology itself is by analogy to what Tomaszewski used for the Sophie Germain counterparts A111153 and A111206.

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 1..498

Chris Caldwell, "Pierpont primes." primeform posting, Oct 25, 2005.

Chris Caldwell, "Pierpont primes." primeform posting, Oct 25, 2005. [Cached copy]

Eric Weisstein's World of Mathematics, Pierpont Prime

Eric Weisstein's World of Mathematics, Semiprime

FORMULA

{a(n)} = Semiprimes A001358 both of whose factors are of the form (2^K)*(3^L)+1. {a(n)} = {A005109(i)*A005109(j) for integers i and j not necessarily distinct}.

EXAMPLE

a(1) = 4 = 2^2 = [(2^0)*(3^0)+1]*[(2^1)*(3^0)+1] = A005109(1)*A005109(1).

a(2) = 6 = 2*3 = [(2^0)*(3^0)+1]*[(2^1)*(3^0)+1] = A005109(1)*A005109(2).

a(3) = 9 = 3^2 = [(2^1)*(3^0)+1]*[(2^1)*(3^0)+1] = A005109(2)*A005109(2).

a(4) = 10 = 2*5 = [(2^0)*(3^0)+1]*[(2^2)*(3^0)+1] = A005109(1)*A005109(3).

a(5) = 14 = 2*7 = [(2^0)*(3^0)+1]*[(2^1)*(3^1)+1] = A005109(1)*A005109(4).

a(6) = 15 = 3*5 = [(2^1)*(3^0)+1]*[(2^2)*(3^0)+1] = A005109(2)*A005109(3).

MATHEMATICA

Select[Range[10^3], Plus @@ Last /@ FactorInteger[ # ] == 2 && And @@ (Max @@ First /@ FactorInteger[ # - 1] < 5 &) /@ First /@ FactorInteger[ # ] &] (* Ray Chandler, Jan 24 2006 *)

CROSSREFS

Cf. A001358, A003586, A005109, A055600, A111153, A111206, A113432, A113434.

Sequence in context: A236108 A253106 A320969 * A115654 A036326 A078972

Adjacent sequences:  A113430 A113431 A113432 * A113434 A113435 A113436

KEYWORD

easy,nonn

AUTHOR

Jonathan Vos Post, Nov 01 2005

STATUS

approved

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Last modified March 5 15:57 EST 2021. Contains 341825 sequences. (Running on oeis4.)