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A307790
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Number of palindromic heptagonal numbers with exactly n digits.
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2
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3, 1, 1, 2, 1, 1, 3, 0, 0, 1, 4, 3, 2, 0, 1, 0, 1, 1, 2, 2, 2, 2
(list;
graph;
refs;
listen;
history;
text;
internal format)
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OFFSET
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1,1
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COMMENTS
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Number of terms in A054910 with exactly n digits.
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LINKS
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G. J. Simmons, Palindromic powers, J. Rec. Math., 3 (No. 2, 1970), 93-98. [Annotated scanned copy] See page 95.
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EXAMPLE
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There are only two 4-digit heptagonal numbers that are palindromic, 3553 and 4774. Thus, a(4)=2.
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MATHEMATICA
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A054910 = {0, 1, 7, 55, 616, 3553, 4774, 60606, 848848, 4615164, 5400045, 6050506, 7165445617, 62786368726, 65331413356, 73665056637, 91120102119, 345546645543, 365139931563, 947927729749, 3646334336463, 7111015101117, 17685292586717, 19480809790808491, 615857222222758516, 1465393008003935641, 8282802468642082828, 15599378333387399551, 20316023422432061302}; Table[Length[Select[A054910, IntegerLength[#] == n || (n == 1 && # == 0) &]], {n, 19}]
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PROG
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(Python)
def afind(terms):
m, n, c = 0, 1, 0
while n <= terms:
p = m*(5*m-3)//2
s = str(p)
if len(s) == n:
if s == s[::-1]: c += 1
else:
print(c, end=", ")
n, c = n+1, int(s == s[::-1])
m += 1
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CROSSREFS
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KEYWORD
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nonn,base,more
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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