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 A136113 Pentagonal numbers > 0 which are not the difference of two larger pentagonal numbers. 6

%I

%S 1,5,12,35,51,92,117,176,330,477,782,852,1080,3876,4347,7526,7740,

%T 9801,13776,14652,22632,24512,27270,39285,69876,85562,88452,103622,

%U 124272,137562,144926,193142,220992,268182,315792,343922,354051,403782,523626

%N Pentagonal numbers > 0 which are not the difference of two larger pentagonal numbers.

%H Donovan Johnson, <a href="/A136113/b136113.txt">Table of n, a(n) for n = 1..500</a>

%F a(n)=A000326(A136112(n)). A number m is in this sequence iff A136114(m) = 0 iff A136115(m) = 0.

%e a(1..3)=P(1),P(2),P(3) since these cannot be written as difference of 2 other pentagonal numbers > 0.

%e P(4)=22=P(8)-P(7), therefore P(4) is not in this sequence.

%o (PARI) P(n)=n*(3*n-1)>>1 /* a.k.a. A000326 */

%o isPent(t)=P(sqrtint((t<<1)\3)+1)==t

%o for( i=1,999,for( j=i+1,(P(i)-1)\3, isPent(P(i)+P(j))&next(2)); print1(P(i)","))

%Y Cf. A000326, A136112-A136118.

%K nonn

%O 1,2

%A _M. F. Hasler_, Dec 15 2007, Feb 07 2008

%E a(34)-a(39) from _Donovan Johnson_, Sep 05 2008

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Last modified August 11 22:58 EDT 2022. Contains 356067 sequences. (Running on oeis4.)