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A332989
a(n) is the smallest number writable in n different ways as the sum of two distinct nonzero pentagonal numbers.
8
6, 211, 2999, 13352, 205427, 250927, 1134927, 2177527, 5002427, 6422352, 17349697, 30135652, 45997927, 55075502, 168570052, 130917177, 101275552, 249483677, 441561407, 433742427, 771789552, 1546505052, 1316582177, 1701923302, 2288827477, 1073520852, 3110207127
OFFSET
1,1
COMMENTS
I conjecture this sequence is infinite.
LINKS
EXAMPLE
211 can be written 35 + 176 and 1 + 210;
2999 can be written 852 + 2147, 247 + 2752, 117 + 2882;
13352 = P(52) + P(79) = P(29) + P(90) = P(17) + (93) = P(10) + P(94).
PROG
(PARI) a(n) = for(k=1, oo, if(sum(i=1, sqrt(1+12*k)\6, sqrt(1+24*k+12*i-36*i*i)%6==5)==n, return(k))); \\ Jinyuan Wang, Mar 06 2020
CROSSREFS
Cf. A093195 (analog sequence for perfect squares).
Sequence in context: A093536 A002037 A071367 * A370128 A030265 A275567
KEYWORD
nonn
AUTHOR
Olivier Gérard, Mar 05 2020
EXTENSIONS
Name clarified by Jinyuan Wang, Mar 06 2020
Terms a(12) and beyond from Giovanni Resta, Mar 08 2020
STATUS
approved