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A333012 Integers which can be written in exactly two ways as a sum of two distinct nonzero pentagonal numbers. 4
211, 215, 381, 447, 602, 663, 766, 807, 853, 874, 1002, 1172, 1197, 1248, 1259, 1372, 1427, 1457, 1571, 1612, 1622, 1639, 1652, 1665, 1752, 1862, 1927, 1996, 2047, 2152, 2245, 2297, 2302, 2332, 2351, 2415, 2472, 2497, 2506, 2523, 2618, 2887, 2912, 2952 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
EXAMPLE
211 = P(5) + P(11) = P(1) + P(12) = 35 + 176 = 1 + 210, where P(n) is the n-th pentagonal number A000326.
PROG
(PARI) is(k) = sum(i=1, sqrt(1+12*k)\6, sqrt(1+24*k+12*i-36*i*i)%6==5) == 2; \\ Jinyuan Wang, Mar 06 2020
CROSSREFS
Sequence in context: A031780 A036232 A064826 * A136601 A108406 A051268
KEYWORD
nonn
AUTHOR
Olivier Gérard, Mar 05 2020
STATUS
approved

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Last modified June 24 19:44 EDT 2024. Contains 373690 sequences. (Running on oeis4.)