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A155565 Intersection of A001481 and A020669: N = a^2 + b^2 = c^2 + 5d^2 for some integers a,b,c,d. 1
0, 1, 4, 5, 9, 16, 20, 25, 29, 36, 41, 45, 49, 61, 64, 80, 81, 89, 100, 101, 109, 116, 121, 125, 144, 145, 149, 164, 169, 180, 181, 196, 205, 225, 229, 241, 244, 245, 256, 261, 269, 281, 289, 305, 320, 324, 349, 356, 361, 369, 389, 400, 401, 404, 405, 409, 421 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

Contains A155575 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) isA155565(n, /* use optional 2nd arg to get other analogous sequences */c=[5, 1]) = { for(i=1, #c, for(b=0, sqrtint(n\c[i]), issquare(n-c[i]*b^2) & next(2)); return); 1}

for( n=1, 500, isA155565(n) & print1(n", "))

CROSSREFS

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

Sequence in context: A010437 A020682 A243702 * A278336 A051216 A255978

Adjacent sequences:  A155562 A155563 A155564 * A155566 A155567 A155568

KEYWORD

easy,nonn

AUTHOR

M. F. Hasler, Jan 25 2009

STATUS

approved

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Last modified June 13 10:28 EDT 2021. Contains 344985 sequences. (Running on oeis4.)