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A136113 Pentagonal numbers > 0 which are not the difference of two larger pentagonal numbers. 6
1, 5, 12, 35, 51, 92, 117, 176, 330, 477, 782, 852, 1080, 3876, 4347, 7526, 7740, 9801, 13776, 14652, 22632, 24512, 27270, 39285, 69876, 85562, 88452, 103622, 124272, 137562, 144926, 193142, 220992, 268182, 315792, 343922, 354051, 403782, 523626 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Donovan Johnson, Table of n, a(n) for n = 1..500

FORMULA

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

EXAMPLE

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

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

PROG

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

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

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

CROSSREFS

Cf. A000326, A136112-A136118.

Sequence in context: A192303 A066280 A192243 * A050189 A116995 A032281

Adjacent sequences:  A136110 A136111 A136112 * A136114 A136115 A136116

KEYWORD

nonn

AUTHOR

M. F. Hasler, Dec 15 2007, Feb 07 2008

EXTENSIONS

a(34)-a(39) from Donovan Johnson, Sep 05 2008

STATUS

approved

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Last modified May 30 06:51 EDT 2017. Contains 287302 sequences.