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A155568 Intersection of A001481 inter A020670: N = a^2 + b^2 = c^2 + 7d^2 for some integers a,b,c,d. 1
0, 1, 4, 8, 9, 16, 25, 29, 32, 36, 37, 49, 53, 64, 72, 81, 100, 109, 113, 116, 121, 128, 137, 144, 148, 149, 169, 193, 196, 197, 200, 212, 225, 232, 233, 256, 261, 277, 281, 288, 289, 296, 317, 324, 333, 337, 361, 373, 389, 392, 400, 401, 421, 424, 436, 441, 449 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

Contains A155578 as a subsequence (obtained by restricting a,b,c,d to be nonzero). Also contains A000290 (squares) as subsequence.

LINKS

Table of n, a(n) for n=1..57.

PROG

(PARI) isA155568(n, /* use optional 2nd arg to get other analogous sequences */c=[7, 1]) = { for(i=1, #c, for(b=0, sqrtint(n\c[i]), issquare(n-c[i]*b^2) & next(2)); return); 1}

for( n=0, 500, isA155568(n) & print1(n", "))

CROSSREFS

Cf. A001481, A002479, A003136, A002481, A020668 ff.

Sequence in context: A115651 A062559 A010417 * A067252 A227645 A089042

Adjacent sequences:  A155565 A155566 A155567 * A155569 A155570 A155571

KEYWORD

easy,nonn

AUTHOR

M. F. Hasler, Jan 25 2009

STATUS

approved

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Last modified December 22 22:37 EST 2014. Contains 252372 sequences.