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A318530 Numbers that can be written in more than one way as p^2 + q^3 + r^4 with p, q and r primes. 1
145, 210, 637, 754, 2317, 2530, 2917, 5218, 5437, 5890, 6447, 6997, 7469, 7653, 7738, 8650, 9333, 11818, 12417, 12796, 14770, 15178, 15197, 15295, 15513, 16349, 16501, 17367, 18389, 19709 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Robert Israel, Table of n, a(n) for n = 1..10000

EXAMPLE

a(1) = 145 = 2^2 + 5^3 + 2^4 = 11^2 + 2^3 + 2^4 .

The first term which can be written in three different ways is

17367 = 23^2 + 13^3 + 11^4 = 113^2 + 13^3 + 7^4 = 131^2 + 5^3 + 3^4 .

MAPLE

N:= 10^5: # to get terms <= N

P:= select(isprime, [2, seq(i, i=3..floor(sqrt(N)))]):

Psq:= map(`^`, P, 2):

P3:= select(`<=`, map(`^`, P, 3), N):

P4:= select(`<=`, map(`^`, P, 4), N):

V:= Vector(N):

for a in Psq do for b in P3 do for c in P4 do

   s:= a+b+c;

   if s <= N then V[s]:= V[s]+1 fi

od od od:

select(t -> V[t]>=2, [$1..N]); # Robert Israel, Jan 30 2019

CROSSREFS

Subset of A134657.

Sequence in context: A051414 A176699 A177223 * A158133 A094613 A207058

Adjacent sequences:  A318527 A318528 A318529 * A318531 A318532 A318533

KEYWORD

nonn

AUTHOR

Philippe Guglielmetti, Aug 28 2018

STATUS

approved

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Last modified April 10 09:20 EDT 2021. Contains 342845 sequences. (Running on oeis4.)