

A089034


a(n) = (prime(n)^4  1) / 240.


3



10, 61, 119, 348, 543, 1166, 2947, 3848, 7809, 11774, 14245, 20332, 32877, 50489, 57691, 83963, 105882, 118326, 162292, 197743, 261426, 368872, 433585, 468962, 546165, 588159, 679364, 1083936, 1227083, 1467814, 1555421, 2053685, 2166190
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OFFSET

4,1


COMMENTS

Mod 2, odd primes p are 1 and mod 4 or mod 6, p=+1, so that p^2==p^4==1 (mod 2*4*6). Moreover, mod 5, p==+1, +2 for p>5, implying p^2==+1 or p^4==1, so that finally p^4==1 (mod 2*4*6*5), i.e., 240 divides (p^4  1) for p>5.
From JeanClaude Babois, Jan 13 2012: (Start)
From Simon Plouffe's web site we know that sum_{n >= 1} n^3/(exp(2*n*Pi / 7)  1) = 10.0000000000000001901617..., very close to a(1). Extensive calculations suggest that more generally, for any prime p >= 7, Sum_{n >=1} n^3/(exp(2*n*Pi / p)  1) is similarly very close to (p^41)/240.
Victor Miller replied on Jan 29 2012 via email, with an explanation of this observation. The following is an abridged version of his reply:
Let q = exp(2*Pi*i*z). Define the Eisenstein series E_4(z) = 1 + 240*sum_{n >= 1} n^3*q^n/(1q^n). For your observation we take z = i/p, so that q = exp(2*Pi / p). So what you've evaluated numerically is (E_4(i/p)  1)/240.
The Eisenstein series obeys the transformation law E_4(1/z) = z^4*E_4(z), or E_4(i/p) = p^4*E_4(i*p). Your observation reduces to showing that E_4(i*p) is very close to 1. In this case q = exp(2*Pi*p), so E_4(i*p)  1 is bounded by a geometric series in q. In your first case, when p = 7, q is around exp(44), which is already quite small. (End)


LINKS

Charles R Greathouse IV, Table of n, a(n) for n = 4..10000


MATHEMATICA

Select[(Prime[Range[50]]^41)/240, IntegerQ] (* Harvey P. Dale, Nov 28 2015 *)


PROG

(PARI) a(n)=(prime(n)^4  1)/240 \\ Charles R Greathouse IV, May 31 2013


CROSSREFS

Cf. A024702.
Sequence in context: A090373 A218427 A041184 * A261938 A271790 A319965
Adjacent sequences: A089031 A089032 A089033 * A089035 A089036 A089037


KEYWORD

nonn


AUTHOR

Lekraj Beedassy, Nov 12 2003


EXTENSIONS

More terms from Ray Chandler, Nov 12 2003


STATUS

approved



