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A233999 Values of n such that numbers of the form x^2+n*y^2 for some integers x, y cannot have prime factor of 7 raised to an odd power. 3
1, 2, 4, 8, 9, 11, 15, 16, 18, 22, 23, 25, 29, 30, 32, 36, 37, 39, 43, 44, 46, 49, 50, 51, 53, 57, 58, 60, 64, 65, 67, 71, 72, 74, 78, 79, 81, 85, 86, 88, 92, 93, 95, 98, 99, 100, 102, 106, 107, 109, 113, 114, 116, 120, 121, 123, 127, 128, 130, 134, 135, 137, 141, 142, 144, 148, 149 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Equivalently, numbers of the form 49^n*(7m+1), 49^n*(7m+2), or 49^n*(7m+4). [Corrected by Charles R Greathouse IV, Jan 12 2017]

LINKS

Table of n, a(n) for n=1..67.

FORMULA

a(n) = 16n/7 + O(log n). - Charles R Greathouse IV, Jan 12 2017

PROG

(PARI) is(n)=n/=49^valuation(n, 49); n%7==1||n%7==2||n%7==4 \\ Charles R Greathouse IV and V. Raman, Dec 19 2013

(PARI) is_A233999(n)=bittest(22, n/49^valuation(n, 49)%7) \\ - M. F. Hasler, Jan 02 2014

(PARI) list(lim)=my(v=List(), t, u); forstep(k=1, lim\=1, [1, 2, 4], listput(v, k)); for(e=1, logint(lim, 49), u=49^e; for(i=1, #v, t=u*v[i]; if(t>lim, break); listput(v, t))); Set(v) \\ Charles R Greathouse IV, Jan 12 2017

CROSSREFS

Cf. A055046, A055047, A233998.

Sequence in context: A034036 A010410 A010459 * A047350 A319742 A190723

Adjacent sequences:  A233996 A233997 A233998 * A234000 A234001 A234002

KEYWORD

nonn,easy

AUTHOR

V. Raman, Dec 18 2013

STATUS

approved

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Last modified May 14 18:01 EDT 2021. Contains 343900 sequences. (Running on oeis4.)