OFFSET
1,2
LINKS
Donovan Johnson, Table of n, a(n) for n = 1..500
FORMULA
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
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