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A113434 Semi-Pierpont semiprimes which are also Pierpont semiprimes. 3
4, 9, 10, 25, 49, 65, 289 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Semiprimes both of whose prime factors are Pierpont primes (A005109), which are primes of the form (2^K)*(3^L)+1 and where the semiprime is itself of the form (2^K)*(3^L)+1.

No more under 10^50; what is the next element of this sequence?

No more terms <= 10^100. - Robert Israel, Mar 10 2017

This sequence is complete, see Links. - Charlie Neder, Feb 04 2019

LINKS

Table of n, a(n) for n=1..7.

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

Charlie Neder, Proof of the completeness of this sequence

Eric Weisstein's World of Mathematics, Pierpont Prime

Eric Weisstein's World of Mathematics, Semiprime

FORMULA

{a(n)} = intersection of A113432 and A113433. {a(n)} = Semiprimes A001358 of the form (2^K)*(3^L)+1 both of whose factors are of the form (2^K)*(3^L)+1. {a(n)} = {integers P such that, for nonnegative integers I, J, K, L, m, n there is a solution to (2^I)*(3^J)+1 = [(2^K)*(3^L)+1]*[(2^m)*(3^n)+1] where both [(2^K)*(3^L)+1] and [(2^m)*(3^n)+1] are prime}.

EXAMPLE

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

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

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

a(4) = 25 = 5^2 = [(2^2)*(3^0)+1]*[(2^2)*(3^0)+1] = (2^3)*(3^1)+1.

a(5) = 49 = 7^2 = [(2^1)*(3^1)+1]*[(2^1)*(3^1)+1] = (2^4)*(3^1)+1.

a(6) = 65 = 5*13 = [(2^2)*(3^0)+1]*[(2^2)*(3^1)+1] = (2^6)*(3^0)+1.

a(7) = 289 = 17^2 = [(2^4)*(3^0)+1]*[(2^4)*(3^0)+1] = (2^5)*(3^2)+1.

MAPLE

N:= 10^100: # to get all terms <= N

PP:= select(isprime, {seq(seq(1+2^i*3^j, i=0..ilog2((N-1)/3^j)), j=0..floor(log[3](N-1)))}):

SP:= select(t -> t <= N and t = 1+2^padic:-ordp(t-1, 2)*3^padic:-ordp(t-1, 3), [seq(seq(PP[i]*PP[j], j=1..i), i=1..nops(PP))]):

sort(convert(SP, list)); # Robert Israel, Mar 10 2017

CROSSREFS

Cf. A001358, A003586, A005109, A055600, A111153, A111206, A113432, A113433.

Sequence in context: A191905 A113432 A129830 * A236024 A141395 A121215

Adjacent sequences:  A113431 A113432 A113433 * A113435 A113436 A113437

KEYWORD

nonn,fini,full

AUTHOR

Jonathan Vos Post, Nov 01 2005

STATUS

approved

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Last modified August 20 14:06 EDT 2019. Contains 326152 sequences. (Running on oeis4.)