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 A155716 Numbers of the form N = a^2 + 6b^2 for some positive integers a,b. 20
 7, 10, 15, 22, 25, 28, 31, 33, 40, 42, 49, 55, 58, 60, 63, 70, 73, 79, 87, 88, 90, 97, 100, 103, 105, 106, 112, 118, 121, 124, 127, 132, 135, 145, 150, 151, 154, 159, 160, 166, 168, 175, 177, 186, 193, 196, 198, 199, 202, 214, 217, 220, 223, 225, 231, 232, 240 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Subsequence of A002481 (which allows for a and b to be zero). Primes are in A033199. - Bernard Schott, Sep 20 2019 LINKS David A. Corneth, Table of n, a(n) for n = 1..17743 (terms <= 10^5) MATHEMATICA With[{upto=240}, Select[Union[#[[1]]^2+6#[[2]]^2&/@Tuples[ Range[Sqrt[ upto]], 2]], #<=upto&]] (* Harvey P. Dale, Aug 05 2016 *) PROG (PARI) isA155716(n, /* optional 2nd arg allows us to get other sequences */c=6) = { for(b=1, sqrtint((n-1)\c), issquare(n-c*b^2) & return(1))} for( n=1, 999, isA155716(n) & print1(n", ")) (PARI) upto(n) = my(res=List()); for(i=1, sqrtint(n), for(j=1, sqrtint((n - i^2) \ 6), listput(res, i^2 + 6*j^2))); listsort(res, 1); res \\ David A. Corneth, Sep 18 2019 CROSSREFS Cf. A002481, A033199. Cf. A000404, A154777, A092572, A097268, A154778, A155707-A155717, A155560-A155578. Sequence in context: A154681 A225676 A030764 * A025002 A120136 A020743 Adjacent sequences:  A155713 A155714 A155715 * A155717 A155718 A155719 KEYWORD easy,nonn AUTHOR M. F. Hasler, Jan 25 2009 STATUS approved

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Last modified January 23 01:48 EST 2020. Contains 331166 sequences. (Running on oeis4.)