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A135771
Terms in A136112 which are not in A135768.
4
5, 23, 51, 71, 72, 99, 123, 239, 263, 311, 359, 479, 599, 699, 743, 863, 911, 1031, 1103, 1151, 1431, 1563, 1583, 1823, 1851, 1863, 2111, 2543, 2663, 3023, 3119, 3191, 3291, 3671, 3719, 3863, 4131, 4203, 4271, 4463, 4671, 4703, 5039, 5231, 5351, 5391, 5399
OFFSET
1,1
COMMENTS
Pentagonal-Indices of terms in A136113 which are not in A135769.
A135768 resp. A135769 are subsequences of A136112 resp. A136113; the present sequence gives the indices of the elements of the former which are not in the latter: A136113(A135771(k)), k=1,2,3,... are the pentagonal numbers P(m) which are not the difference of two pentagonal numbers P(n)-P(q) with n,q>m, but only with n>m>q. A136112(A135771(k)) are the corresponding indices of the pentagonal numbers.
LINKS
FORMULA
Equals the difference set A136112 \ A135768.
EXAMPLE
The first terms of this sequence correspond to the following elements of A136113:
P_5 = P_7 - P_5,
P_23 = P_24 - P_7,
P_51 = P_66 - P_42,
P_71 = P_74 - P_21,
P_72 = P_80 - P_35,
P_99 = P_104 - P_32,
P_123 = P_144 - P_75,
P_239 = P_249 - P_70,
P_263 = P_274 - P_77,
P_311 = P_324 - P_91,
P_359 = P_374 - P_10.
PROG
(PARI) P(n)=n*(3*n-1)/2
isPent(t)=P(sqrtint((t*2)\3)+1)==t
{for( i=1, 999, for( j=1, i-1, isPent(P(i)+P(j))|next; for( k=i+1, (P(i)-1)\3, isPent(P(i)+P(k))&next(3)); print1(i", "); next(2)))}
CROSSREFS
KEYWORD
nonn
AUTHOR
R. J. Mathar and M. F. Hasler, Feb 07 2008
STATUS
approved