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 A256613 Numbers D such that D^2 = A^3 + B^4 + C^5 and A^2 + B^3 + C^4 = d^2 for some positive integers A, B, C, d. 7
 7, 9, 17, 55, 72, 96, 459, 616, 1536, 4125, 9504, 11875, 19551, 36864, 64881, 67392, 77824, 108000, 171699, 262656, 388869, 559776, 786375, 1052672, 1081344, 1160000, 1413872, 1459161, 1850202, 1936224, 2530971, 3264000, 4158189, 5187500, 5238816, 6533679 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Subsequence of A256091 such that A^2 + B^3 + C^4 = A180241(k)^2 for some k. For A=2^(2n+2), B=2^(2n+1), C=2^(2n), n=0,1,2,... one has A^2+B^3+C^4 = 2^(4n) (16+8*4^n+16^n) = d^2 with d = 4^n (4^n+4), and A^3+B^4+C^5 = 2^(6n) (2^(2n)+8)^2 = D^2 with D = 8^n (4^n+8). So the latter represents an infinite subsequence (9, 96, 1536, ...) of this sequence. LINKS EXAMPLE (A, B, C) = (1, 4, 2) = 1^3 + 4^4 + 2^5 = 1 + 256 + 32 = 289 = 17^2 and 1^2 + 4^3 + 2^4 = 1 + 64 + 16 = 81 = 9^2, so 17 is a term. PROG (PARI) is_A256613(D)={my(A, C=0, D2C5); while(1

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Last modified August 17 23:13 EDT 2022. Contains 356204 sequences. (Running on oeis4.)