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A056581 Nearest integer to 1/(A056580(n)-exp(sqrt(n) pi)). 7
-7, -51, 4, -2, -5, 110, 15, -3, 3, 5, -7, -3, 19, 4, 5, -3, 430, 141, 4, 4, -2, 574, 3, 7, 1518, -3, 62, 84, -2, -10, 11, -7, -13, -4, 4, -3, 45551, -5, 3, 3, 2, -33, 4494, -8, -5, -6, 3, -2, 7, 2, 9, -3, -4, -4, 3, -17, -2, 5624716, 147, -5, 4, 3, 3, 2, 6, -2, 747638 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

A measure of how close e^(pi*sqrt(n)) is to an integer (higher absolute value of a(n) means closer, negative value means the closest integer is smaller than it).

The sign convention is chosen so that most terms and in particular record values such as those occurring for the Heegner numbers A003173, are positive, so that A069014 lists record indices of this sequence (except for A069014(2)=2 instead of 3 for signed values). The sequence is not defined for n=0,-1 where e^(sqrt(n) pi) is an integer. - M. F. Hasler, Apr 15 2008

Negative resp. positive values of a(n) correspond to 2nd resp. 3rd term of the continued fraction expansion of exp(sqrt(n) pi), up to a difference of -1 or -2 depending on the direction of rounding. - M. F. Hasler, Apr 15 2008

REFERENCES

For links, references and more information see A019296 and other cross-referenced sequences.

LINKS

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

FORMULA

a(n)=1/(A056580(n)-e^(sqrt(n)*pi)).

A019296 ={-1, 0} U { n | abs(A056581(n)) >100} U { some n for which abs(A056581(n)) =100 }. - M. F. Hasler, Apr 15 2008

EXAMPLE

a(6)=110, since e^(pi*sqrt(6))=2197.99087 and 1/(2198-2197.99087)=109.52 which rounds to 110.

e^(pi*sqrt(163))=262537412640768743.99999999999925007259719818 (the Ramanujan number) and so a(163)=1333462407513.

PROG

(PARI) default(realprecision, 100); dZ(x)=round(x)-x

A056581(n)=round(1/dZ(exp(sqrt(n)*Pi))

CROSSREFS

Cf. A003173, A019296-A019297, A035484, A056580, A058292, A060456, A069014, A138851.

Sequence in context: A197890 A320989 A015495 * A039308 A029525 A037500

Adjacent sequences:  A056578 A056579 A056580 * A056582 A056583 A056584

KEYWORD

sign

AUTHOR

Henry Bottomley, Jun 30 2000

EXTENSIONS

Definition, formulas and values corrected and extended by M. F. Hasler, Apr 15 2008

STATUS

approved

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Last modified August 14 09:14 EDT 2020. Contains 336480 sequences. (Running on oeis4.)